He is 18 in Sly 1 and 21 in Sly 2 and 22/23 in Sly 3.
yes he was married to carmelita in the end of sly 3 ya ding dong
No one knows, as a sly 4 hasn't come out yet.
in sly 2 the clock work pieces were stolen by the claw gang and sly has to stop them and get all of clockwork