i went to windells a couple years ago when i was 18. i had already been a freshman in college. i went with my brother and cousin, who were both younger than me. since i didn't want to be by myself in the "adult" house, i stayed with my brother and cousin in the oldest house you could without being an adult. it was like 15 - 17 year olds i guess. and i'll be perfectly honest, i felt a little too old for it.
windells was pretty fun, don't get me wrong. trampolines were ill, food wasn't bad, cool to ski in the summer. i didn't get to go over to the adult house but i heard it was pretty fun. they have a hot tub and stuff.
windells does have a lot of younger kids around. by age 21, like if i were going now looking back on it, i'd be kinda ehh about it.
if i were you, i would kinda maybe save it for a getaway with your friends or something. like go to park city, or aspen, or wherever you want. because if you think about it, windells is like what, probably 1,900 or so now plus a flight? you could go to these places and spend probably 1,000 - 1,500 and have a nice week of skiing and lodging and food (then you have to buy a flight still, but whatever.) but then you get to do whatever you want, you're not on any schedule or anything, and what not.
but then again, i didn't get exactly the same experience as the other "adults." but i was there after all, so i kinda know what's up.
pm me if you have any questions.