I don't get it. They just stay in the hero business as they get older?
Essentially, yeah.
The fun of doing something like this, as in Generations, is to explore the passing of the torch, to invent legacy heroes that take over for the originals. Heck, that used to happen a lot in Marvel, at least with the Avengers and X-Men. If it's just the same heroes getting really old, that seems to squander the potential of the premise.
Tony Stark mentions that there are younger heroes during the Civil War chapter, and he talks about how they differ from Peter and Steve Rogers, but we don't ever see them in this story. Events generally conform to 616 history, except with characters aging in real time, with a few exceptions. Carol Danvers appears to have adopted the Captain Marvel title in this universe than she did in the 616. Something weird happens to Vision. (Given the time period of that part, it feels like a reference to the Distinguished Competition.) But the story isn't about the other heroes or about their legacies. It's about Peter Parker and why he carries this burden (both physical and emotional) of being Spider-Man from his teens into his seventies.
Let me add, I agree with you -- one of the best things about Generations was seeing the mantles passed, the next generation taking the place of their forebears. But that's also a fundamental DC idea; they leaned into the heroic legacies for a long, long time. Marvel historically hasn't been as big on doing the heroic legacy. When they do pass a mantle, it's going to return to its original owner pretty quickly.