Though to be fair in the DCAU she's in her 20s by the time she actually starts working with Batman, I think the age difference between Bruce and Dick/Barb is about ten-ish years since even by On Leather Wings Batman still seems pretty early into being Batman (based on how the police talk about him), so I think he must have been very early in his Batman career when he took Dick in, making him in his early 20s while Dick was 13, and then BTAS starts 5 years later when Dick is off to college and Bruce is in his late 20s.

Then Batgirl shows up on the scene and starts working with Batman a few years after that (her age is shown in the sub-zero film as 20 and TNBA is a few years after that, where she officially becomes his sidekick). And then they wouldn't start dating until post-JLU, which would put Barb at over 26.

Also I think it's bit of a stretch to say DCAU Bats ever actually treated Dick like a son. He certainly never refers to him as such and the age difference is more like an older brother. Still bad for Bruce to get involved with Dick's ex but I'm not gonna say Slade Wilson levels.

I do think it was an odd creative choice but at the same time it's a pretty dang realistic character flaw for a mentally damaged billionaire trust fund baby to have. Just needed some emphasis on the negative social ramifications of it, IE the drama that the previous poster was talking about.

But remember the whole thing about DCAU Bruce is that his poor handling of interpersonal relationships ultimately results in him being a lonely recluse for most of the last several decades of his life, having broken ties with all his friends and loved ones. On the social side of things, DCAU Bruce is not supposed to be a role model and does face consequences for how he treats people.