I know people don't really consider them Hip-Hop, but isn't one of the dudes in LMFAO like 37? Also, Rick Ross didn't hit it big until he was 30.
When I first seen Smoke DZA rapping I thought he was some dude from the 90's who never made it big.... then I find out he's still in his 20's
But Yeah anything over 35 and just breaking out on the scene is too old.