I've lived with one kidney for over 40 years. I had cancer when I was a mere babe, and at 14 months old I had one removed. As I was so young I can't compare the difference with/without but for most of my life I have done sports ok - and never been told that I shouldn't.
Unfortunately, recently, my second one is failing too, so at some point it will be dialysis for me and maybe a transaplant if I'm lucky enough. The docs seem to think I should be ok for another 10 years or so the way I am at the mo, before the serious stuff kicks in.
Out of interest how does having one kidney affect you day to day life if you don't mind me asking? Is it ever a hinderance or is it kinda always on the back of your mind etc? Just curious.