Because it is an easy outdoor activity that is challenging but does not require a lot of physical movement for the older persons. It is competitive, yet you are not going to get a broken ankle unless you are a dumbass.
I didn't hear about such an announcement. But he said before more than twice that he'd think of retiring after season 2007/08. But I'm sure that he is capable of performing in his top form for two more seasons to come. Don't worry, Juventus will extend his contract.