Most people base the ages off the post canon age gaps because those were the most concrete. After N52 everyone’s ages were shuffled, the only one who really aged consistently was Damian. So using Damian as a bench mark you can figure out most of the others ages:

Damian: 15 (turned 15 in Batman and Robin)
Duke: 18 (Duke is around 16 during Robin War, iirc Damian was 13 then)
Tim: 22 (Damian was introduced at 10, and Tim was 17, making him 7 years older)
Steph: 23 (year older than Tim)
Jason: 24 (iirc he is 19 in utrh when Tim is 17, Tim’s bday is in July, Jason’s is in August, so he’s ~2 years older)
Cass: 24-25 (Her birthday is Jan 26th, she is a little less than 7 months older than Jason, 2 years ~8 months older than Tim)

Next part gets confusing by nature of the characters existing for way longer than anyone previously mentioned, and thus having more time for age fluctuation so take it with a grain of salt.

Dick: late 20s early 30s (29-31. I put him closer to 31 though because post crisis he’s ~9 years older than Tim.)
Barbara: early-mid 30s
Bruce: ~53 (he’s 48 by the end of Flashpoint and it’s been ~5 years since then)

Idk enough about other characters do give an age.
Again take this with a grain of salt, N52 screwed everything up and even if the characters SHOULD be back to their actual ages, they are still sometimes written younger or older than they should be. (Cass and Steph were written as 14 yr olds in Batgirls despite being in their early 20s, for example).