I think he looks a lot older than other heroes.

I'd say mid to late 30's atleast but no older than 50

forty something

Post-Quiver, about late 30s. Pre-Quiver, mid 40s.

He should be well into his fourties. He was definitively in his 40s in the Mike Grell books, but he got de-aged by an unspecified amount when he came back to life. Still, I seem to remember his de-aging to be about 10 years, and it's been almost ten years since Quiver came out (not that comic time = real time).
 
Additionally, look at Connor Hawke. Connor must be in his 20s, and Ollie was in his 20s when he conceived Connor. That's probably part of the reason Connor isn't in the new series. He seems to be much younger in the current run than he was in GA & BC. He played the role of a father in that series, though, so that contributes some to him seeming older in that book.

I picture him at 41 years old.