If you compare the MM wireframe with the OoT wireframe of child link, MM Link is slightly taller. The added abilities (hylian shield, flips, bow, hookshot... MM link knows the whole arsenal like the back of his glowing yellow hand) add weight to this arguement- he's gotten stronger and improved his talents. And though I generally avoid using official art as a basis for presumption, the MM art makes link look a bit older (which fits with the much more mature context of MM). As a whole, I'd say less than a year, but more than a season has passed between MM and OoT.
We can assume that aLttP and LA Links, while not being fully adults, are not terribly young either. LA Link was doing a pretty good job of handling his ship, until it got hit by lightning, and his maturity in LA is that of a veteran. Similary, the aLttP Link is generally treated like an adult... we can again fall to studying art to guess that aLttP Link is fairly old (looks to be about 16 by my reckoning).
The Four Swords games are trickier. Assuming they follow the same Hero, then we need a relatively short period of time between each game, probably something along the same lines as OoT/MM. The reason for this is that we need time for things to settle down between the games.
Minish Link is proably the same as WW Link, which I have always assumed is 12. I have a brother who's twelve, and he makes the same girly scream whenever I push him into lava that WW Link does.

Good times.