i saw your post in passing and couldn't help myself....
"if it's got balls or brakes, it's gonna be trouble"
never too old. i raced BMX state titles in my first year of racing at 40. i placed 4NSW among younger women....and after a health and other random stuff hiccup, i'm back racing, at 45.
downhill sounds like a hellava lot of fun tho. go for it, Smiffy.