On the subject of people staying on when they are way past their best
I think it depends on several things
obviously enjoyment to the sport is key - same for any sport - I heard of an ex top line England rugby player who was still playing for his club many years later - he was down to the 5th team but stayed on coaching and playing where he could contribute - and helping the bar profits!
but if they feel they can contribute by changing their training so be better able to be a domestique or pulling long turns on the front then I would admire that if they want to do that
However some just can;t do much that they feel is worth it - or have other priorities - look at Nico Rosberg in F1 - won the championship then just buggered off and spent time with his family that he had neglected for years to get where he was.
Horses for courses and all that
anyway - enough woffle - I'll go now