I'm sorry, but you're nearly 21...I was married at 22. I've been going on holiday alone/with friends (camping) since 15. Spent a week in a b&b with my gf age 17. First holiday abroad at Uni, which was late by most: A lot of people go on a gap year before Uni. 18. A lot of people study abroad, a year of living on your own in a different country <20.
Why do you even ask your parents? I don't reacall ever consulting them before doing stuff after my 16th birthday!
Go on holiday. Tell them about it. If the "decide" you're not going... maybe it's time to move out (I assume that's the only reason they have so much input).