Early 20s? 30s? Batman seems to be in his early 40s and that kinda stuck out to me

The ages are never mentioned or hinted too except for Cyborg but I'd assume they're the same age as their comic book counter parts so they're all in their early / mid twenties, save for Cyborg.

Before the time skip, he is 22-24.

http://www.comicvine.com/forums/justice-league-of-america-630/the-official-ages-of-the-members-of-the-justice-le-681506/

No way is Batman in that movie in the 20-30 range.

Way.

XD. Yea, it's the animated version of a known-comic arc. All of the heroes had not been operating long at that point.