Watching DS9 lately, something I've occasionally thought about is how old to consider Odo. It's easy to just thinking of him like René Auberjonois and consider him as being mid-to-late 50s throughout the series. But that doesn't really make in-universe sense. He's a Changeling, and doesn't age like regular humanoids. He's probably looked the same way nearly as long as he's been taking a humanoid form. Really, Changeling age is a much trickier thing since they aren't born the same way as regular life forms, either. You could look at when he split off as his own entity, but for my purposes here I don't think the time he spent floating around in space or as an unexplained specimen counts.
So when did Odo start to communicate with others? What's his early timeline? Well, that's not quite clear. Memory Alpha says there was a line cut from the first episode that may have referred to his discovery being in 2337 (about 32 years before that episode), but of course... the line didn't happen. What we know for certain is he was studied at the Bajoran Institute of Science for seven years before leaving on his own. One episode with a flashback to 2365 has Gul Dukat talking about seeing Odo presented by scientists a couple years earlier, ~2363. If that was near the end of the seven years, that might suggest experimentation on Odo began around 2356. Counted from there, Odo would be 13-20 throughout the run of DS9!
Of course, once again a direct comparison to human age isn't really appropriate. Surely Odo's early years weren't analogous to early human years, and him striking out on his own after seven years is very different than a 7-year-old kid going out on their own. So for lack of anything better, let's say Odo going off on his own after getting sick of being a test subject puts him in a similar place to a humanoid getting to the age where they can legally go off their own, screw that dumb school and parents! Which varies from place to place, but let's say in 2363 Odo was in a similar place to an 18 year old human. If we age him a year for a year past that, in his time on DS9 (the show, rather than the station) he'd be 24-31. Young, but just a couple years below Kira.
I think recognizing Odo for the young being he is, both in physical experience and emotional state, makes him a more believable character on the series. His inexperience with interpersonal relationships and desire to know about his origins fit more with a young man than a 50-something.