It's about average that you guys are 17. TBA 2006 means the release date will be revealed sometime in 2006. It doesn't mean it's going to be released (the game) in 2006, just the release info. So lets figure by the way blizzard works, they say it's going to be released Q1 2007. Thats already 2 years from now. You're all going to be around 18-20. Figure it gets delayed for a year (like ALMOST every blizzard Game has (notice I said game, not expansion)) -- Thats another year tacked onto that. 19-21. I'm sure you guys will still be playing Diablo, or better yet, have an intrest into Diablo when that time comes around.
****, I'll even do the math for the 15 year olds here. You're going to be around 17-19. You're not going to want to spend all your time playing a "little kiddy game" anymore. You're going to have better things to do, like play WC3 still, or drool over the thought of a SC2.