First of all. Just because you found out your dad smokes, doesn't mean that he has to allow you to smoke. Your parents can smoke ciggs and drink a bottle of vodka a night, it doesn't mean they will let you do it.

Why were you looking in his closet? If you have a good reason for being there and weren't simply snooping I would simply tell him why you were there and what you found. Depending how he responds to that, point out how he obviously doesn't buy into the propaganda as so many do, and ask him if your mom knows he smokes? If she does, ask him if he would talk to your mom and see if she would allow you to smoke.

Other than that, it is up to their discretion. You are still under their roof, and am guessing you are under 18. If I had a child, I would not "allow" them to smoke until they were at least 16 and than other factors would also be taken into account.

Grades, personality, maturity level.