I never really thought about rewarding one of my sons just because he'd reached a certain age. I did give my oldest son a pristine, 70 Series GC when he graduated college. GC was owned by my father, who died in '81. More recently gave him a G21, so he'd have something better for home defense.
Gave my daughter a G26 when she got into law school; likewise my youngest son, when he got into law school. Built a nice M4 with Daniel Defense barrel, NM RRA trigger, etc., when he passed the bar exam. When/if my youngest ever gets a good gun safe, I'll probably give him the other lnib 70 Series GC that I have in my safe...has only had one mag shot through it.