This isn't a "should they age" thread, or a "what fits in their continuity" thread. When you look at the characters in the titles you read (or remember), without doing any math, how old do you figure that they are?
For me:
Superman's about 30-35.
Batman's about 35.
Nightwing is about 25 or 26
Batgirl is about 28 or 29
Robin is about 14
Wonder Woman: there's no telling because she's immortal, but she physically looks under 30
Wonder Girl is about 15
Flash (Barry) is about 30
Flash (Wally) I'm not sure anymore, but he's about Nightwing's age
Green Lantern (Jordan) is somewhere between 28-32
Green Lantern (Stewart) is about 35-40
Green Arrow is about 30
Speedy/Arsenal/Red Arrow/Whatever is about 26
Martian Manhunter: there's no telling
Black Canary is between 28-30
Hawkman and Hawkwoman are both (relatively) about 35
Black Lightning is about 32