I'd say Kit was somewhere between 11 and 12 during Plunder And Lightning and was 12 by Flight School Confidential (which I'd say was some time later considering most episodes were not day by day, some could have been).

Molly 5 or 6 at the stard, definitely 6 by Molly Coddled (by it's structure that episode happened over some time and was said near the end).

I'd say Baloo and Karnage are in there late 30's early 40, like what KitCloudkicker52885 said Karnage claims to be 29 but a lot of self-absorbed megalomaniac's who aged well say that.

Rebecca early-mid 30's possibly late 20 but most likeley the former.

Wildcat I'd say mid-late 20's, he seems more youthful.

Kit is 12

Molly is 6

Most of the adults in the series are in their early, mid and late 30's

Like Baloo and Rebecca, I would say they are in their mid 30's, or at least Baloo is, Rebecca could be in her early 30's

Don Karnage could be in his late 30's or early 40's, though he claims to be 29

Louie and Wildcat are presumably the same age as Baloo.

Well Kit and Molly's age I know for sure but the rest I just guessed or assumed from the way they are drawn and animated and from they way they sound and acts.

In case you want to know, I'd guess Shere Khan to be in his mid 40's

Hope this helps.

The other fans could correct me but I believe that Kit is 12 (mentioned in one episode) and Molly is 6. As for the other characters, I'm not sure even the creators of the show had put a definite age on them (though you may still try to ask Jymn in the "Ask the creators" section)