... based a bit on this week's Flash tie-in of the current multiversal nonsense over in DC, but mostly on Frank Miller's — and you can see his yucky thought-fingerprints in that
comic — vision of a Bruce getting older or already old.
In Miller's eyes, Batman wins, he's Batman, because he's preternaturally macho. He's tougher, stronger, faster, and gruffier (and also richer and whiter, by the way) than everybody else. He's testosterone with a cowl, driving a tank with bats drawn on it. He's the goddamn Batman. Bruce Wayne might shave as often as he wants, the stubble comes with the cowl.
So what happens when the goddamn Batman starts getting old? He keeps working out of course, builds himself an exoskeleton, puts larger weapons on his tanks, gets himself a very young, naive, and very female Robin, and generally speaking has a late middle age crisis. Because if who you are is solely based on your raw physical power, then getting older has to be maddening. Demeaning. Humiliating.
Miller's Batman, at some level, goes cuckoo because he's afraid one day some punk will out-lift him at the gym, and a journalist-and-or-lingerie model will go out with him.
Now, my Bruce... He's the World's Greatest Detective, you know. One of its greatest tacticians. A scientific polymath. He routinely defeats metas who are stronger, faster, tougher than him by a much larger factor than what separates a human at twenty from that same person at sixty. Make him, say, a seventy-years-old guy who's independently mobile and deceptively skillful at knowing where to hit you with his cane to very painfully disable you, but who of course would never willingly get himself in a place where that's going to be part of his plan, and you don't get a septuagenarian in an oversized bat-themed exoskeleton.
You have a detective who figured out 99% of everything fifteen seconds after he arrived, who has the personal number of and is owed favors by pretty much everybody in the planet with some sort of significant power or specialized skill, who can organize a very complex manhunt with his eyes closed and be waiting for you with a cup of tea at the place you thought nobody would find you.
And, yes, maybe he has with him a bodyguard with a discrete yellow "R" pin somewhere on his or her clothes, there to taze and/or kick your ass. But it could also be a whole SWAT team, or a kryptonian, or whatever will work best for that particular situation.
A Bruce Wayne who has, however unwillingly, given up on the whole dress-like-a-bat-and-personally-punch-crime-on-its-face approach is, and I know this is one of my pet peeves, a much more dangerous man. It could also be interesting for him to keep his physical skills: a Bruce Wayne who Gotham thinks is a clumsy playboy, but Jim Gordon knows is secretly the best damn consulting detective in the world (although useless in a fight), and the JLA knows is secretly also a genius tactician and engineer (but not somebody you send to a fight) would be funny, but it'd be even funnier if now and then a bad guy *swore* Bruce Wayne went all Shiva on him, and the Gotham comedy shows made a night out of it, Jim Gordon chuckled at the idea, and a giggling JLA asked J'onn to stop doing it. J'onn doesn't say anything, because he finds the whole thing as amusing as I do.
But I got distracted. In summary: A Bruce who can no longer fight worth a damn is one who's going to make sure you're toast *before* anybody has to fight you. If you're lucky, you'll find yourself financially broke and tied up in maddening unrelated problems before you got all the pieces of your plan in place, without a clear idea of how the hell that happened.
If you're less lucky, you'll be threatening Gordon to kill all the hostages, and then he'll add to the phone call somebody who'll tell you a lot of things about your past and your present you thought nobody could know, and he'll mention the names, current locations, and personal phone numbers of some people you *really* don't want to know those things, and before Gordon has to empty his pipe you'll be asking the guy if releasing the hostages will be enough to get him to back off or if he wants something else, just please don't do it.
If you're really unlucky, or happened to orphan somebody, he's probably not going to be anywhere near you, yet you're going to be writhing in pain from a very specific and totally untraceable accident for a couple of hours before the cops find you.
Bruce Wayne's held back by those physical skills of him, that's what I'm saying. Separate the crime-fighting from the fantasies of hypermasculinity, and physical frailty won't slow him down.
(PS: Batman Beyond is an interesting middle point: he stopped being Batman, but he never moved into being something else. A different sort of broken, I think.)
(PS 2: I wrote some stuff about Babs here, for obvious reasons, but that spiraled into something way too long, less structured, and incredibly more hairy, as, ultimately, Bruce has 99% of all textual and meta-textual privileges ever given to any human or fictional character, while Barbara, well. She's a badass, and, in a Borgesian way, I think she has often beaten *the writers*.)