It’s difficult to tease out how much of that sort of thing is genetic vs a function of their remote training history.
We see this is weightlifting too. People who were laborers or competitive weightlifters when they were young for many years, suddenly start lifting again after like a decade long break. They progress rapidly and are beating younger people pretty soon.
There are some extremely long-term (permanent?) muscle structural changes that are induced by long term weightlifting, and when these people go back to sport, they have the advantage of just “reactivating” these things.
I would presume the same is true with endurance sports like cycling. Would explain why the “floor” is so much higher in people with remote long-term riding histories.