My crush is going to aks me out but i have to say no...?

ok there is this guy in my school that says he fancies me. he is popular. i am not!. he is got lots of friends, and i don't!. my parents are VERY stricted about dating and would never let me date until i am 18. i really like him but i have to say no because i know that my parents would never allow me to date cuz they think it would disrupt my studies and my Future career path. i really like him and if he does ask me out what do i say???. i don't really want to say no but i know i definitely have to cuz of my parents! and it sucks!