We know that Captain America was born in 1918. However, his serum slows down his aging process. My question is, how old exactly is Captain America at the end of Avengers: Endgame,
after he comes back as an old man?
Captain America was born July 4, 1918. The events of Endgame take place in 2023. He then time-jumped from 2023 back to 1948 and lived his life until ending up back in 2023.
In cumulative time, this makes him approximately 180 years old at the end of Endgame.
Captain America was frozen in the year 1945 aged 27. He was defrosted in the year 2011 and lived until 2023, then looped back around to 1948. He then lived (unfrozen) until 2023.
His cumulative unfrozen time is approximately 114 years.
I have a theory. We know that Peggy Carter dies in 2016, as seen in the MCU. At that point, I think that Captain America decides to return to the original timeline some time before he leaves, so that he can be on the bench. This gets rid of the discontinuity between timelines, and stuff like that. It also makes him 7 years younger than most estimates, as well as having him skip the Snapture. This means that unlike most answers say, he is actually 107. Added on to this the serum, and he is probably in his biological mid 80's. While the theory is my own, it also makes sense, as he knew that Peggy would die in 2016, and probably wanted to avoid the Snapture.