is it confirmed is any source ?

@xargo: In the Pre-52 he was 225 million years old.

@dondave: how..wut…cant even….WHO IDEA WAS THIS?!? how old were his kids?!? 50'000

@dondave: that's a great fact right there

@dondave: Well now that is what I call old... :D

@dondave: I'm wondering how old he is post-flashpoint

with his new origin he could be like 8 years old

Hundred of millions if not billions of years old.

If I'm not mistaken the latest reports from NASA say that Mars lost its atmosphere around 2 billion years ago. So if we are to take that into account, then J'onn puts the O in old.

@heavenlydarkdragon: this is so very mind boggling, again he didn't need to be this op, i wouldn't have minded a century or two, but 225,00000 years old?!? i know pre crisis isn't the worst but what hell were they thinking

Much of his history was created Post-Crisis (including the above page by John Ostrander), as his past was not delved into very much outside of his adventures prior to Crisis. Currently looking for further sources for this claim, since this is a passing reference that could be missed by an editor and the rest of the production staff. There doesn't seem to be anything outside of his eponymous title that references anything that closely approximates his age. Best I can find is that there are references to him being "centuries old". Also that he will likely live into the 30th Century (this one is Pre-Crisis, as seen in Superboy and the Legion of Super-Heroes #200). Other references indicate that Martians had very long lives to begin with, but nothing specific to how long. The number 225 is obviously a reference to his first appearance in Detective Comics #225, but I've seen no references indicating that he is millions of years old outside of John Ostrander's single text box. What I'd like to find is something further in cannon that clarifies - at least generally - how old he currently is or how long Martians' life expectancy is. It's also possible that J'onn also has added life force which enhances his life expectancy, but - again - I find no indications of this. Also, If anyone has another page reference or the like that will help nail this down, I'd appreciate it. It's possible that DC has ignored this particular reference to a specific level of nigh-immortality, even though it's been generally accepted that he is extremely long lived. But I'd like to see more than one reference, as Who's Who in the DC Universe makes absolutely no mention of this particular aspect of his Martianhood. Thanks!