In their 20s most likely.

Depends on the member. And the continuity. In terms of publication history, they have been around for 65 years. Before Flashpoint rebooted the multiverse, Dick and those who were his age were in their late 20s by the time New Earth ended. Younger members of later incarnations were obviously younger. At present, we just had another soft reboot that altered some characters ages, although to what extent, we do not know. New Earth did a better job at giving checkpoints in terms of ages.

Dick, Wally, Roy and the others who were original Titans are probably in their late 20s. In Infinite Frontier, Raven and Gar's age was altered so I think both of them are in their early 20s. Tim's generation are still teenagers/young adult. Damian is also a teenager, according to Teen Titans Vol 6. Emiko and Wallace are probably older than Damian.

At the start of Rebirth, Damian was 13 while Wallace was 15. Perhaps that age difference is still in place, putting Wallace at 16 since Damian is 14. Teen Titans Academy #1 even featured Dick’s birthday, but the writer Tim Sheridan didn’t note his age at all.

Wally west listens to music from the 90s and is offended when the music is called old (see latest issue of the flash) so I’m assuming the original Titans are currently late 20s/early 30s.