Unless Red Skull finds a time portal, I wonder how he'd come back without having aged significantly since his last encounter with CA? I mean unlike CA, he wasn't frozen or put into sleep for the last 70 years.
As Captain America says in the film, the serum basically enables him to keep healing at a rapid pace, which would also slow down the aging process. Red Skull's body didn't react well with the serum, but that doesn't mean he didn't get to keep some of its benefits. How else could a guy with a burnt face survive and not die from any number of infections?