Ir'a Never Too Late
I turned 56 this week (not so happy about that!). I work an office job sitting at a desk and computer all day every day, which is not conducive to being fit and had gained a lot of weight in the past 10 years, which I am now slowly but surely taking off!!
I started riding my bike about a year ago, but only once or twice a month and only in perfect weather and easy rides. In May of this year I purchased a Trek road bike and started riding 50-75 miles a week. I started on the Silver Comet Trail in Georgia which is flat, no cars and pretty easy and graduated to road rides and now taking on longer rides with more hills (I hate hills). I also take spinning classes at least twice a week and in bad weather.
My only issue is that I get really tight in my muscles no matter how much I stretch before/after the ride, so I have started yoga classes to help with stretching and flexibility. It's also lots of fun 
I also do weight training (light weights!) twice a week mostly for my upper body.
I think over 50 you don't just jump on a bike and compete with the youngsters, you need to work your way up and really focus on your overall fitness, flexibility and strength. This will help to prevent injury, because we don't bounce back so fast from that.
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"I never made "Who's Who"- but sure as hell I made "What's That??..."