I see a reference to age discrimination under Swiss law which says:
The prohibition of age discrimination is a fundamental right guaranteed by the Swiss Federal Constitution (Article 8, paragraph 2: No person must be discriminated against due to their age). As a fundamental right, it binds the state and the authorities towards individuals. It thus applies to employment relationships governed by Swiss public law (e.g. members of the civil service).
I also see on their website that the university in question (below) is a public university in Switzerland (so I would assume Swiss public law would apply):
USI, sometimes referred to as the University of Lugano, is one of the 12 certified public universities in Switzerland coordinated by swissuniversities.
So, how could it be that this job add is not a violation when it starts with the following text:
The Faculty of Informatics of the Università della Svizzera italiana (USI), located in beautiful Lugano, Switzerland, invites young researchers to apply for an Assistant Professor position.