Like any former pro athletes, some of them get fat and lazy. Others stay in pretty good shape.
A number of ex pros have done very well in L'Etape de Tour, which is not riding the actual TDF, but still takes pretty good shape to be at the pointy end.
It's an incredibly demanding lifestyle to race at the Pro Tour level. It's unreasonable to expect anyone to stay at that level of fitness when their careers are over. That said, most old pros could still drop most of all of us at will.
I don't think anybody here wants a sprint against Cippolini, even at his advanced age.
http://cyclingperspective.com/mario-...pollini-bikes/