What's interesting to me is how nicely the DC Animated Universe avoids this problem. I've found that it holds up very well if you assume each series (except the ones set in the future, of course) takes place in roughly the years it aired. My conjectural DCAU chronology has Bruce Wayne born in 1962, becoming Batman in 1984 at age 22. Dick Grayson is born in 1974 or '75 ("Robin's Reckoning" is ambiguous about whether he's 9 or 10 in his flashbacks, which are early in Batman's career). B:TAS begins around 9 years later, in 1993 (at least the Robin episodes thereof, since FOX insisted Robin be 18), so Bruce is 31 and up. He's around 37 by the time of TNBA, 39 by the start of Justice League, 43 by the end of JLU. It's a reach to assume he could still be physically capable at 43 after two decades of extremely strenuous activity; realistically he'd have burned out in his early 30s. But he's supposed to be the ultimate physical specimen and all, and some pro athletes (like Jimmy Connors) have managed to keep competing professionally into their early 40s. So I think it's within acceptable limits.
Actually, if you take 'Epilogue' into consideration it lines up even better as Waller says at some point, not long after JLU, she notices Bruce start to slow down with age before retiring after about another 20-30 years. And only then because he has a heart attack right in the middle of a fight.
Actually I think he retired because the only way he got out of the fight he had a heart attack in was to point a gun at the guys he was fighting.