I looked him up on Wikipedia, and apparently he's still alive because his armor has some sort of life-sustaining powers. Far-fetched, yes, but not impossible. And as for the Widow, I'm not sure it IS necessary - at least, not at this point. She was introduced as a Cold War-era Russian spy, and later as a Soviet defector. That was, of course, perfectly fine at the time, given that the Cold War was still going on, and it's still pretty much fine now - the Cold War ended in '89, about twenty years ago now. Sure, having an anti-aging formula inside her would make sense, given that she still looks like she's in her thirties, but that would still only make her about fifty, if you fudged things a little and pretended that her introductory story took place in roughly '85, and that she was in her mid-twenties then. She could skate on the whole 'ex-Soviet spy' thing for another decade or so, then be retconned into simply being ex-KGB, an organization that still exists, as far as I know. It's a little sneaky, sure, but comics do it all the time - there's nothing in her history saying that she HAS to have been a contemporary of Captain America.