I dont think you are ever too old to jump. If your doc says you are in decent shape I dont think you are ever too old.
But here is a video of a 5 YEAR OLD skydiving!!
http://broadbandsports.com/node/26616
I think this is pretty badass but how old should someone be before they can make the decision on whether it is worth the risks? This is obviously not in the US but should we let young kids go if their parents okay it?