Anyone who tries to tell me Bruce was younger than 24 when he started will get nothing but laughter. We know from Nightwing 153 that Babs is old enough to wish she was 22 again, so the late-20s to early-30s might be fairer to her, and guess that she's maybe 5 years older than Dick (it would be old enough to make Babsgirl/Robin as weird as it was, but not as bad when it was Oracle/Nightwing)?
Confusing the issue further, according to a conversation Tim and Babs have in Cry For Blood (which is nine year old now, but who knows how long in comic book time), Helena's family was killed when she was eight, which was stated to be "roughly fifteen years ago". The "roughly" bit is probably to be intentionally vague, so I'm tempted to add a few years to it, because I find it hard to believe Helena could be my age at the time, considering she'd not only need to have finished college and gotten a teaching job in Gotham (simultaneously training the whole time) and establish ten years worth of comics afterward. She debutted around the time Babs stopped being Batgirl, so she should be around the same age if not older, but never really comes off that way. Putting her older than Dick is certainly no problem, as he doesn't mind older women (hi Babs!), but that still doesn't settle things. Whether anything in Huntress: Year One settles or further confuses this I couldn't say.
The only tangentially related character whose age I can confirm is Renee Montoya, who turned 29 in Tec 747 (cover dated August 2000) and a show of her passport in 52 give her a birthdate of Sep 7, 1970. I have a problem though, believing that she's been The Question for three (or even one!) years, so we'll just keep it to 36-7, but, not knowing her age in relation to anyone else, that doesn't really help matters for the Batfamily as a whole.