There are several policy goals surrounding the age of criminal responsibility. One aspect is that by the age of criminal responsibility people have a sufficient awareness of societal norms and understanding of the wrongfulness of their conduct that they be eligible for criminal charges. Another aspect is that for people under the age of criminal responsibility, they may not respond to criminal charges and punishment in the same way as older people. That is, the criminal system may not be the most effective means of correction and rehabilitation of such young offenders.
There is no bright line that accurately captures these factors, and thus many jurisdictions have more than one step in transitioning from the incapable child to the fully capable adult. For example, in the US and Canada, juveniles/youth over the age of criminal consent but not yet 18 years old are generally not treated the same as adults.
The policy goals behind the age of consent relate to understanding of the consequences of sex, vulnerability to people in positions of power or influence, and protection of society's norms of purity.
There is no reason why these different policy goals would result in the same age threshold.