I read somewhere that in the Zelda - OoT manga, Child Link is 14, which would make his adult incarnation 21. That sounds the most feasible to me. As child link seems to have much more stamina than most of the aforementioned ages (<13), but still has a childish appearance which does not support claims he could be 16 or over.
Similarly, with Adult link, 21 sounds the most reasonable, whereas 17 sounds too young for him to be considered "Adult" Link, and 23 sounds a little too old, but still possible for his appearance (this however could not be the case, since it would make his younger incarnation 16, which would be too old).
