I didn't see Back to the Future until I was an adult.
My most-watched movies are probably Old School, Eurotrip, and Dude Where's My Car. I'm not big on rewatching movies, but those I watched many times in my youth. I haven't seen Eurotrip as an adult yet, the other two I watched again in the last couple of years.
Dude Where's My Car? Well that was unexpected. I have to say I kind of enjoyed that movie as well especially the fight over the back tattoos.
Were you alive when BTTF was released? That could be a good reason why you didn't see it until you were an adult if that is the case.
That type of humor shaped me a lot as a young boy. It was just too laugh-out-loud funny and it still holds up to this day. I love Sean William Scott and Ashton Kutcher both.
Dude... Sweeeeet!
I wasn't born until 1992, so no I wasn't alive when BTTF came out.