OoT Link is like 18, TP/SS Link around 16/17. (That puts OoT Young Link around 11, and MM Link probably 12 or 13)
I remember an interview that said that TP Link was the oldest one.
OOT Link is 16, it was in Iwata Ask.
Straight from Iwata Asks,
Yes. When we decided to handle Link growing up from a 9-year-old child to a more mature 16-year-old, I wanted lots of characters to fulfill various roles. For example, Kaepora Gaebora is a grandfather figure who gives Link all kinds of advice and looks out for him. And since Link is a boy, I wanted girls besides Princess Zelda to show up.
http://iwataasks.nintendo.com/interviews/#/3ds/zelda-ocarina-of-time/4/1