The MCU is coming off about a decade of focusing on Cap and Iron Man and moving forward the universe will get to explore more characters from the comics including with the Eternals, Shang-Chi, Blade and at some point maybe the X-Men and Fantastic Four since Disney has the rights to those characters now.
Apparently Old Man Cap was 112 years old in that scene, meaning he was probably just about one hundred around the time that the events of The Avengers occur.
It’s true that by the time the OG Steve Rogers got carved out of the ice, the other one would have already been the happy old man who gives Anthony Mackie’s Sam Wilson his shield.