Here is a photo of my oldest snail. I adopted him in July 2009, he came from Petsmart. No idea how old he was when I got him, but he's been with me for eighteen months now.
click for full-size imageThe outer layer of his shell started to flake off in December 2009. I tried applying a nailpolish patch over the original area, which you can still see today - it's the purple splotch on his backside. Needless to say, covering the original area didn't actually halt whatever has caused this. His original colouring is a dark striped snail, possibly dark striped olive. Nowadays he looks like a giant gumball that has been sucked on for a while.
In spite of this perpetual shell problem, he soldiers on, 18+ months and counting. He's a bit old and crotchety acting, he sleeps a bit more than the younger snails, but he comes out a few times every day and explores the aquarium. He's the biggest snail in my tank now, and not as quick as some of the younger ones... so he frequently finds himself on the receiving end of some of the younger males' affections.
When I first got him, I named him Little Buddy. Incidentally - I used an early picture of him when I made my forum avatar picture. He was so small back then...
click for full size imageThis is one of my younger snails, hatched last summer. He's playing on the artificial plants. I call the plants 'trees' as they have a stout thick 'trunk' and then a crown of foliage ontop. The snails all seem to enjoy climbing and hiding in the leaves. This one has found his way to the very top of the 'tree' (about 17 or 18 inches high) so for the moment, he's king of the aquarium.

Cheers!