Post Doc application form in France asks for very personal details, is it normal?
No, it is not &quot;normal&quot;. According to the French labor code:

Les informations demandées, sous quelque forme que ce soit, au candidat à un emploi ne peuvent avoir comme finalité que d'apprécier sa capacité à occuper l'emploi proposé ou ses aptitudes professionnelles.
Ces informations doivent présenter un lien direct et nécessaire avec l'emploi proposé ou avec l'évaluation des aptitudes professionnelles.

Translated by myself:

The only purpose of any question asked, under any form, to a candidate for a job must be to evaluate their ability to perform their work duties or to evaluate their professional aptitude.
These questions must have a direct and necessary link with the offered job or with the evaluation of professional aptitude.

It is straight up illegal to ask these question (and it has been since at least 2008). You shouldn't answer them, and provide them a link to the labor code (and perhaps offer to call the labor inspectors to clarify the situation) if they get upset. Your age, your marital status, your possible children have no bearing on your ability to perform your duties as a postdoc (there are some exceptions, postdoc is certainly not one of them).
Now, is it &quot;normal&quot; in the sense that it is the norm? Employment law is unfortunately not the best-respected law around here...