Finally some people are speaking without the narrow mindedness of a few of the posters here. If the lad wants to turn his life around and become an aviator he should have every oportunity. I know many pilots who have dabbled in illicit use of drugs in thier pre flying lives and many are successful and happy pilots, having left thier mistakes behind.
If he gives up the wacky weed for good and can pass the required testing then good luck to him.