I can see TT losing "tween" and teens due to them thinking it is a "baby" game. But younger ages LOVE the game. I mean, its like walking and talking in their own cartoon! And you have to remember with every kid comes an adult, hence another possible player, lol.
I have a neice who is barely driving age who still plays. Maybe she doesn't admit it to her friends but she loves playing. I don't think TT will die out anytime soon.
And really it isn't a "baby" game. It can get quite difficult.
Also, I just had another neice join last week. Yay!