Random question that I thought of while trying to sleep. What do you think the Rogues' ages were when they either started being costumed criminals or started being a team?
This is all pre-Flashpoint, because post-Flashpoint is particularly a mess from an ageing and continuity perspective.
Axel was 16, and Owen was 19. This information came from creators in interviews.
Roy got his prisma-goggles when he was 21 and he probably didn't become the Rainbow Raider immediately, but he probably wasn't significantly older than that.
Evan is particularly challenging because he was seemingly de-aged during his history. Originally, I'd say he was kinda old, probably somewhere in his 30s when he became the Mirror Master. By the Johns era, he was probably in his early twenties when he started.
I want to say that Al Desmond was ~25 when he became a costumed criminal. He was stated to be "over 30" during the Bronze Age, though in those days there wasn't really a compressed timeline like we have now so who knows how much time had passed in-universe. He was also probably older than the other (or most other) Silver Age Rogues because he likely had significant education by the time he became Mr Element.
The others are a bit harder to figure, IMO. Mick had a job with the circus before he became Heat Wave, and was clearly an adult when he debuted. He was also stated to be 40 during Johns' run, so I think it's pretty likely he's one of the older Rogues. And Len of course looked ancient by then, though he'd had a lot of hard living so he wasn't necessarily that old. Digger was balding before he became Captain Boomerang, although some men start balding pretty early so it also doesn't necessarily mean much. But I tend to think of these guys as the oldest core Rogues, even if it's kinda based on vibes more than anything. I'll say ~25 for them too.
Mark is probably on the older side of the Rogues as well, as he was showing his age in the Johns era and had a well-established burglary record and stints in prison by the time he became the Weather Wizard. Maybe 23-24 when he started?
Sam was such an enigma that I really don't know what to think. He did look kinda craggy sometimes, and he also had a well-established burglary record and stints in prison before becoming the Mirror Master. He was also someone the other Rogues naturally looked to and accepted as leadership material, so he might have been a bit older than all the core Rogues. That's my feeling, at any rate, so maybe 26 or over.
Len called Hartley "kid" at an unspecified point, and Hartley said he was "thirty-plus" around the time it was mentioned that Mick had turned 40. Mind you, "thirty-plus" could be a coy way of saying "39" (it's technically correct!), so I wouldn't necessarily think Hartley was significantly younger than Mick. We know that Hartley was kicked out of several colleges before he became the Pied Piper, so he was probably a young adult when he debuted.
(And one thing to be kept in mind is that some people call others "kid" to condescend to them, so it could be an indicator of age or it might just be another Rogue being a jerk to his peer)
James was probably one of the younger Rogues when he debuted, likely starting in his late teens or very early twenties. I'll split the difference and say about 20.
Lisa already had a career as a headlining skater in an ice show by the time she became the Golden Glider, so I'd guess she was somewhere past 19, probably in her early 20s.
One hill I'll die on is that Roscoe was very young when he first became the Top. He was arrested only twice before becoming a supervillain even though we know he wasn't a very skilled thief, and he had something of a babyface when he had the idea to become the Top. It probably took a while for him to teach himself to spin and invent his tech, so maybe he was ~22 when he debuted?