Steve Rogers saved the world on multiple occasions, sacrificed his happiness and lost damn near everyone he loved. As such, it was difficult to begrudge his decision at the end of Avengers: Endgame to use the trip to return the Infinity Stones as an opportunity to travel back in time and live in domestic bliss with Peggy Carter, the love of his life. After taking the long way round to get back to the present, Rogers was an elderly man. Still, for someone chronologically pushing a hundred-years-old, he was in relatively good shape due to long-term effects of the super-soldier serum.
But now fans are theorizing that it wasn’t just the serum that preserved him and that Rogers might be functionally immortal. Not just that, but there’s a chance that he could regain his youth.
Now, I’ve got to say that Rogers certainly didn’t look immortal in the finale of Endgame, so where’s this theory coming from? Well, some of it is based on Steve being worthy enough to wield Mjolnir when battling Thanos and that continuing to grant him power. This theory is based in the one-shot comic book 2099: Manifest Destiny. Here, Rogers is frozen once more, waking up in the year 2099 and meeting Miguel O’Hara (aka Spider-Man 2099). Thor’s absent in this time, so Cap takes Mjolnir, which is shown to give whoever wields it eternal life. Perhaps those powers remain with him even after he’s not physically wielding the hammer?
Another way Rogers could remain alive is if the MCU introduces “The Apples of Idunn,” which help keep the Asgardian characters from ageing. Though honestly, them being present in the MCU seems unlikely given that Odin was obviously ageing significantly by the time he died in Thor: Ragnarok.
But could all this lay the seeds for Chris Evans’ Steve Rogers to make a triumphant return one day? Possibly, but Evans has repeatedly said that he’s done with the character, that he’s happy he got such a great ending and it’d feel like a cash-in to bring him back. Heroes like Iron Man and Captain America forever returning is a great way to kill all tension in your fictional universe, so I hope Marvel Studios honors the dramatic impact of Avengers: Endgame and if they do return, it should only be via small cameo appearances here and there.