World War II heroes.

[BWPS]

Cap was frozen during WWII, they thawed him out. etc...
Bucky was also frozen underwater after getting exploded, Russians got to him, etc.
Red Skull was in an exploding building which luckily contained some kind of gas that froze him.

Nick Fury and his Howling Commandos are still said to have been from WWII...
Nick Fury was captured and given some kind of anti-aging potion which he has to drink to stay young, so he's been around since WWII the whole time?
Namor is the same Sub-Mariner from WWII, because he lives longer than humans, or is the current Namor his son?
But I can't find any information about why Dum Dum Dugan and any other living Commandos, if any, are still the same age from WWII. Maybe they all got frozen somehow?

[GhostMachine]

Sub-Mariner is the original. As you said, he ages slower than humans.

The Blazing Skull is apparently immortal.

The original Human Torch (who is still "dead" last time I checked) is an android.

Spitfire originally gained her powers from a transfusion of the original Human Torch's artificial blood, and another transfusion in the Namor series (before it turned to crap once Byrne left) rejuvenated and de-aged her from an old woman to a teenager. However, I think she's portrayed as being physically 18 or in her early 20s now - I didn't read the last Invaders series, but that's more or less how she looked to me when she popped up in Captain America a year or so back.

I assume Dugan and other Howling Commandos who are still around use the same Infinity Formula that Nick Fury uses to stop aging.

Bucky wasn't exactly frozen underwater; when the explosion that supposedly killed him happened, what really went down is that his arm was blown off and he fell into the water and a Russian sub conveniently happened to be in area; he was recovered and brainwashed (he also had amnesia, but that may have been a result of the explosion), and they kept him suspended animation when he wasn't out assassinating people as the Winter Soldier. Cap used a Cosmic Cube to undo the brainwashing and restore his memories. Its also been retconned that he was 18, not 14 or whatever, whenever he became Cap's partner. (His gun use is NOT a retcon; its just something that was ignored by Marvel when they revived Cap and did any WW2 flashback stories until they brought him back as Winter Soldier)

Other WW2 era heroes who are still around and are the original character, not a replacement, I am not really up on regarding how they're not older than dirt.

[Protomorph]

Anyone else reading the new series The Twelve? It seems that 12 MORE WWII era heroes were also frozen by Nazi scientists were found and thawed out in Today's world. Pretty good so far, but they're only on issue 4 of 12. More than a few of them are finding it really hard to adjust.