The Bucket List premiere is actually one of the ones I've been to and I can confirm that Jack Nicholson signed for ages, shook hanRAB, and was well worth the wait. If you can get to a Jack Nicholson premiere, I do recommend it.
There weren't many young people there, though, you're right about that. From what I remember the crowd were older than usual, mostly over thirties. It made for a nicer premiere though - not so much of the usual pushing, shoving and screaming.