Can i enter a giveaway if i am under 18 but i have parental permission?

Hello!
I would like to know if i can enter a giveaway if my parents allow me to even if i am 18, and if i can't.. Why not?? Why i can't? If my parents allow me to i should be able right?

from Android Authority Forums http://ift.tt/29pK5ZQ
via IFTTT