Prior to the French revolution, (around 1784) in france, how and at what age could a man become a clergy?

by Itseliote

I have been assigned to write a journal in history class as a high clergy before and up to the French revolution. In my first journal entry, I am 21 (born 1763, journal entry in 1784). I would like to know if there was an apprenticeship to become a clergy, and the age you had to be to be one.

adenoidcystic

I'd also like to know if it was possible for peasants to get into the clergy, or if it was restricted to the upper classes.