U.S federal law specifically but are there other countries that do this and in USA is an affirmative defense possible in these cases where they are tried as an adult?
Defendants who are later accused of a crime committed when they were minor (under 18, or under 21 if the court finds that they had juvenile mental maturity) will be tried under juvenile rules.
That can lead to people almost 90 years old being sentenced to juvenile detention. (A suspended sentence, not least because of the time that had passed.)
[...] On July 23th, 2020, D. was given a suspended sentence of two years of juvenile detention for 5232 counts of accessory to murder and one count of accessory to attempted murder. [...]
In all U.S. jurisdictions (as a matter of constitutional law), if age was an affirmative defense to the crime when it was committed you would benefit from that affirmative defense at trial, even if the trial took place when you were an adult.
In most U.S. jurisdictions (although that rule is not constitutionally required) you are tried as a juvenile in the juvenile justice system for crimes committed as a juvenile. I recall this being done in a case involving a celebrity in Massachusetts, but don't remember who it was.
In the case of serious offenses committed by an older juvenile, prosecutors in many jurisdictions are allowed to try a juvenile offender as an adult anyway, so trying an adult as an adult rather than as a juvenile for one of these offenses wouldn't violate any right of the defendant.
With respect to federal criminal offenses in particular, I don't know how juvenile offenders are handled in the federal criminal justice system period. In part, this is because these cases are overwhelmingly handled under state law, and in part, this is because there is minimal press coverage of these cases which are usually secret for the general public.
How Sentences Are Served
Despite this fact, the place where the sentence was served might be different if you were an adult when convicted than if you were a child when convicted.
Children who are sentenced to incarceration are usually imprisoned in juvenile detention centers rather than adult prisons. But someone who was, for example, convicted of a murder committed at age 15 when he was age 26, would, in all likelihood, serve his sentence in an adult prison rather than in a juvenile detention center that is not equipped to handle adult detainees.
Most U.S. jurisdictions also provide that someone who is sentenced in the juvenile justice system who "ages out" during their sentence is transferred to an adult prison at that time if the sentence has not been fully served by then.
However, that doesn't come up very often, because the percentage of juvenile convictions that leave someone with a sentence so long that they can age out is small, and a large share of juveniles who commit a crime that serious are transferred from the juvenile justice system to the adult criminal justice system for trial in any case.
Statute Of Limitations Considerations
Also, the question of age of criminal responsibility questions can come up only for a handful of federal crimes that would be barred by the statute of limitations anyway.
The default federal criminal statute of limitations is five years, and 13 years old will generally be above the age of criminal responsibility, so for those federal crimes that can't come up. According to the same source the main exceptions in federal law are as follows:
tax evasion or failure to file a tax return — 6 years from the date of the crime
fraud against the U.S. involving $1,000,000 or more —7 years from the date of the crime
bank fraud or RICO predicated on bank fraud — 10 years from the date of the crime
mail fraud — 10 years from the date of the crime
wire fraud — 10 years from the date of the crime
embezzling from a federal institution —10 years from the date of the crime
conspiracy to commit a federal crime — the applicable statute begins to run on the date of the “last act”
immigration offenses — 10 years from the date of the crime.
"capital crimes" (see below).
It would be rare for a middle school age or younger child to commit thee kinds of fraud crimes, and even more rare for someone below the age of criminal responsibility to be in a position to do so, although the immigration offense crime might come up in the case of an unaccompanied minor illegal immigrant.
There is no federal statute of limitations for certain "capital crimes" but again, the cases where a child below the age of criminal responsibility might commit these acts is again vanishingly rare. Most are variations on murder or attempted murder, although a few go beyond that. Federal capital offense include, but are not limited to:
murder committed in a wide range of specific fact patterns relating to matters under the jurisdiction of the federal government, and also destruction of aircraft, motor vehicles, or related facilities resulting in death, civil rights offenses resulting in death, mailing injurious articles with intent to kill or resulting in death, genocide, hijacking aircraft resulting in death, torture resulting in death committed outside the U.S. by a U.S. national or foreign national on U.S. soil, terrorist murder in the U.S. or another country,
sexual offenses against children.
No. If they were younger than 10 (being the age of criminal responsibility) at the time then they do not commit an offence so cannot ever be arrested for it, regardless of how old they are in the future.
It's extremely difficult to prove a negative but this article by a criminal defence solicitor explains that:
If a person is 10 years old or older, they cannot be arrested or charged in relation to an offence that they committed when they were under the age of 10.
No prosecution for things that a person did while younger than twelve
First, if the act or omission happened while the person was under the age of twelve years old, the person will never face criminal responsibility for that act or omission. See Criminal Code, s. 13:
No person shall be convicted of an offence in respect of an act or omission on his part while that person was under the age of twelve years.
Being "tried as an adult"
Canada does not have the procedure of trying young people as an adult. If an offence is alleged to have been committed while a person was a young person (defined as someone between twelve and eighteen), they will be tried as provided under the Youth Criminal Justice Act. See s. 14(1):
a youth justice court has exclusive jurisdiction in respect of any offence alleged to have been committed by a person while he or she was a young person, and that person shall be dealt with as provided in this Act.
Imposing an adult sentence
the Act does allow judges to impose an adult sentence on a youth who is found guilty of a serious offence and was 14 years of age or older when the crime was committed. In fact, prosecutors are obligated to consider seeking an adult sentence when a youth is found guilty of murder, attempted murder, manslaughter or aggravated sexual assault.
Department of Justice, "Sentencing of Young Persons"
See also Youth Criminal Justice Act, s. 64.
Unsure if this is asking about the age of criminal responsibility, or if it's the age of criminal responsibility in U.S. Federal Law, then the child is not liable for the crime if they were not yet 11 years old on the date of the criminal incident. If they are older than 11, but younger than 18 (legal adulthood). The Feds will either recommend the offender to state court systems, begin federal delinquency proceedings, or petition federal court to move the juvenile to be tried as an adult. This determination is typically case dependent and made based off of specific facts related to the case. If delinquency proceedings are used, the child will not be tried in adult court after turning 18 for the same criminal incidents, as this would violate the child's fifth Amendment rights against double jeopardy.
U.S. law considers the age of the defendant at the time of crime when making a determination, so if they were discovered to be responsible after their 11th birthdate for a crime that occurred prior to that same date, they would not be tried, since they were not 11 at the time of the crime. If they are 17 and will turn 18 before the trial, then they would likely be charged as an adult, but would not subject the child to any punishment that would be for a legal adult offender (i.e. if charged with a capitol offense, you cannot use the death penalty if the defendant was 17 at the time of the incident, even if they are 18 at time of trial).
An exception to U.S. Law's preventing Double Jeopardy is the concept of separate sovereigns. This holds that a trial for a crime in state court triggers only for that state. Other states, territories, tribal governments that are separately sovereign, and the Federal Government can all try an offender for the same crime if the crime occurred in their jurisdiction.
It is exceptionally rare that juvenile offenders are tried in the federal level of government as most federal crimes are not something that can't be handled at the state level, OR involve crimes crossing state lines, the latter of which is difficult for a youth, as it usually involves travel methods not readily available to a juvenile. The most likely youth federal crime would likely involve an incident at a branch office of a Federal Government facility. In that case, the child would likely be criminally referred to state law-enforcement to handle.