Link's generally been a teenager/young adult in the earlier games.
The fact is the three best selling Zelda games (OoT, TP, NES Zelda) feature an older, non-child Link.
I don't need a hyperviolent Zelda game, but what's wrong with a Nintendo franchise that is a little darker and cinematic? I don't want a "cutesy" Zelda, I just don't have the patience to stay in that world for 60+ hours. If you're asking me to play a game that long then I need some meat for my grown-up self to chew on.
Nintendo has so many kid/cartoon-centric franchises already anyway ... Zelda doesn't need to go in that direction. Sometimes its smarter to just give people what they want.
To be honest I wouldn't prefer to baby as say Baby Mario vs. Real Mario. Or Baby Samus vs. Real Samus. I didn't like Baby Kong in DKC3 that much either, prefer using DK. I just don't see the appeal.







