Personally, I think that they have pretty much been self-parody since "Tattoo You"/their best years ended with Mick Taylor (the finest musician ever to have been a Stone) leaving the group. So yes, I think that they are too old to go on/record in an artistically-meaningful fashion.
For what they charge to get into their concerts....no! They have enough money....unless Keith has spent everyones share on dope.......and who wants to see old man balls slinging around everywhere on stage!!! LOL! and I even like The Rolling Stones and still feel this way!
Nope, because they still got it in their blood to produce and write more songs, and actually I would love to see them record one more single on the charts before they retire though.