Pellet gun and parents.?

I am seventeen and turning eighteen this upcoming February in 2012. My parents let me get a bb gun when i was sixteen and now i want to get a pellet gun. BUT my parents wont let me. I dont know why either. I am applying for my FOID (firearms owner identification) card this fall and will be getting a real rifle next spring. So are there any reasons you guys can think of why they wont let me get one?