I'll be turning 49 in just a few short weeks time, and have returned to single speed for the first time in 40 years because I have taken up playing bicycle Polo.
Here I am 6 weeks ago having a go at bicycle polo for the very first time: albeit on my mountain bike. I am the old git wearing the waxed jacket and steel toe cap boots, who can barely hit the ball with the mallet or keep up with the play.
http://www.youtube.com/watch?v=D1SveG_W9QM
Now I have converted an old Universal brand BSO MTB into a polo hack. Basically removing the derailleurs and shorting the chain, removing the standard brake levers and replacing them with a dual brake lever for tricycles, so that I can apply both the front & rear brakes with just my left hand while my right hand wields the mallet. I have also cut down the right hand-side handle bar so that it is just long enough to accomodate a standard length hand grip; this prevents me from catching the bar with the mallet shaft when I whack the ball a "good'un."
Six weeks on and I can charge up and down the court single-handed, whilst keeping up with the play, hitting the ball and scoring the odd goal or two.
My Polo hack:
Showing the cut down right handle bar and the dual cable brake lever.