John Byrnes Superman and current Superman are one and the same.
About how much he can live. I think that as long as he is under a yellow sun he will pretty much live for ever. Unless he gets killed or something.
__________________ What is good?--Whatever augments the feeling of power, the will to power, power itself, in man.
What is evil?--Whatever springs from weakness.
What is happiness?--The feeling that power increases--that resistance is overcome.
Not contentment, but more power; not peace at any price, but war; not virtue, but efficiency (virtue in the Renaissance sense, virtu, virtue free of moral acid).
The weak and the botched shall perish: first principle of our charity. And one should help them to it.
What is more harmful than any vice?--Practical sympathy for the botched and the weak--Christianity...
In Superman Prime he just kept getting older and stronger, he got to godlike levels in that story after many hundreds of thousands of years.
In Kingdom Come it was eluded to that he gets stronger, not older...they said Kryptonite doesn't work on him anymore in that future.
And I think it was Dark Knight Returns where Batman comments that Superman dyed his hair grey to fool people into thinking that Clark Kent was getting older.
__________________ When life hands you a bowl of shit, make shit lemonade out of it.
My impression is that Superman will continue to thrive as long as he has our yellow sun to sustain him. Thing is, in about 5 billion years, our sun will swell into a red giant then exhaust all its fuel and become a cold dwarf. So unless Supes migrates to another yellow star (and 5 gigayears should give him enough time to do so, especially if he sees us leaving for a new star), he loses his powers and ages normally (whatever "normally" is for a Kryptonian).
However, in time, all the stars will burn out, and Superman will pass on. But that's okay cuz there won't be any mortals left to save.
I suppose Supes could shift into a younger, parallel universe (Marvel's?), but what's the point? I would think that after countless eons he might realize it's time to move on from the physical plane. In far less time than a few billion years, us ordinary folk will perhaps have evolved to a higher plane. Conceivably, we could even leave Superman in the evolutionary dust.
I propose that it may be his very attachment to his superhuman identity which may, in the end, keep him "prisoner" in that form (hmm, now wouldn't that be an interesting story...)
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Shinier than a speeding bullet.
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Humans are afraid of the dark.
And yet… At the same time, we’re fascinated and bewitched by it.
Maybe that’s why humans drink the darkness that is coffee.
I get the feeling he'd get killed by something before that happened. That's billions and billions of years away; he's only thirty something now and he's encountered dozens of villians with the potential to kill him, and at least one (Doomsday) who is known to be more than capable of it.