My 12 y.o. son enjoys Mark Lowery. Mark is a Christian singer/comedian, so many of the songs he does are Christian. He does do some parodies of both Christian and secular songs and his comedy runs the gamut, but is always clean. Some of his routines are hilarious.
It’s too bad you can’t get him anything risque, or Tenacious D would be perfect. But I’d recommend against Ray Stevens, just because he might not be that funny or “cool” now.