He’s sowing his wild oats.
More Traditional Proverbs:
A lion sleeps in the heart of every brave man.Traditional
Where the law is uncertain there is no law.
Traditional
Student gets tuition dollars by asking for 0.01 from each person via newspaper.
Traditional
A man stands taller when he stoops for a child.
Traditional
Busy as a bee.
Traditional
It is better to finish something than begin.
Traditional