You probably don't want the book "Cycling Past 50" anyway. I have it and it's really more for hard core riders who want to continue to race after 50. It mainly goes into specific and detailed physiologic explanations why getting old sucks and basically advises to HTFU. (which is always the standard and good advice when it comes to cycling).

However there is a place for over 50 riders right in these forums! It's called the Fifty Plus forum, of all things:

http://www.bikeforums.net/forumdisplay.php?220-Fifty-Plus-(50-)