If we limit the definition of pop music to what charts I think it makes all the sense in the world that it is a young person’s game. So much of what drives chart success is what is in fashion at the time. Trend setting will always be the domain of youngsters.

If we expand the definition of pop music to all music that isn’t classical/jazz/experimental, etc. then older, more experienced musicians should be able to do quite well. Frank Sinatra honed his craft over the decades. I think the stuff he did in his 40s and 50s is probably his best.