Alphinaud, Alisae, and Lyse are teenagers. The Twins spent 1 year on the First so they might be in their 20s by now. Tataru might be a teenager or in her early teens.
Papalymo seems to have been in his 30s or 40s.
Y'shtola seems to be in her 20s, but she acts like she's in her 30s so maybe she is? Spent like 3 years on the First IIRC.
Urianger seems to be in his 30s. Spent like 3 years on the First.
Minfillia couldn't have been any older than 23 or 24 by ARR. In the 1.0 Ul'dah intro cutscene which takes place 10 years before 2.0, she's a little kid, no older than 13 or 14.
Thancred: In the 1.0 Ul'dah intro cutscene (which takes place 5 years before 1.0 takes place, which takes place 5 years before 2.0 takes place), Thancred looks exactly the same as he does today. So assuming he was 18-20 years old back then, and at least 10 years have passed, then he should be at least 30 by the time of ARR. Then he gets isekaied to the First and was there for 5 years, so he should be either in his mid to late 30s, or possibly his 40s. The Shadowbringers cinematic makes him look like he is in his late 40s or 50s. It's bizzare because he still looks like he is in his early 20s ingame.
Krile seems to be in her 20s.
Nanamo seems to have been a teenager or in her early 20s.
Merlwyb seems to be in her 30s.
Kan-E-Seena appears to be in her 20s but might be older due to magic or immortality or something.
Raubahn seems to be in his late 40s or 50s. The Ala Mhigo civil war against the Mad King began 25 years ago (Garlean conquest was 20 years ago), and in Stormblood 4.0 we get a flashback to when Raubahn and Illberd were first recruited to join the war against the Mad King, and they looked to be in their 20s.
Hien and Aymeric seem to be in their mid to late 20s, possibly early 30s.
The game is extremely vague on how much time passes over the course of the story, but by Shadowbringers 5.1, at least two years must have passed since ARR. After ARR 2.0, the Doman Resistance makes their move and try to revolt and fail. The Doman refugees travel by ship from Doma to Ul'dah, a voyage that would have taken months. In Stormblood, the heroes travel by ship from Limsa to Kugane multiple times, and that voyage takes months. You also had Thancred and Estinien travelling to Garlemald and back on foot during the story, which would have taken months. So the Twins and Lyse are almost certainly in their early 20s by now.