I think the reason some people took shots at the Rolling Stones or other sixties rockers continuing to perform in their fifties and beyond was primarily because "rock music" was so closely and firmly associated in their minds with youth and rebellion.

Blues never was. Blues, jazz, adult contemporary, country, etc tend to be more understood as "ageless musics". I'm not saying they necessarily are, just that the media and to a certain extent the performers market them as such. [Stereotypically] rock is about live fast, die young and leave a good looking corpse.

Martha Bayles talks about this at length in her book "Hole in Our Soul".

"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming

Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.