I was around 12 when the original came out, and not mature enough to handle ladder play. With SCII I think anyone who enjoys having to think a bit will love SCII. The major difference with it and BW is that it's a lot more accessible for lower level players. With BW if you weren't a twitch-gamer capable of doing lots of things at once, you lost. With SCII, even if you're a bit slower, the mechanics are way easier and it's more decision oriented.
My gf who never played anything except Mario Galaxy loves it and we'll be picking up an extra copy for her. I think the Blizz magic in it is being able to show casual gamers what hardcore oriented gaming is. It won't redirect people who have 0 dedication to learning a skill and thought process to it, but for people who have the potential but never knew about it, SCII will take them in nicely.
Don't get me wrong, most gamers who don't enjoy long learning curves will hate this, but if you take a few hours to learn the basics & maybe play with a friend who knows something, you will come to love SCII. It's kind of like Chess in space.
I never played WoW but SCII brings forth emotions that no other game has in a long, long time... which I'm guessing is why so many people are addicted to WoW. During the beta downtime I wasn't able to play any other game, they're all so boring and layerless.