some say that because your under 18 you need to honor your parents if they don't want you to practice you shouldn't but there are ways around that. like learning astronomy cooking and mythology
but I too am under 18. im in the broom closet (wiccan term for haven't told anyone I practice.) I keep my Book Of Shadows on a hidden file on my flash drive. a lot of people have a lot of different views on this topic but I think you should do what you fell best but just remember everything could have repercussions
my advice try it for a year, learn the holidays, beliefs, and history not just the magic (if you learning wicca/paganism) then if you like it tell you parents if you find its not for you no harm do not telling anyone.