Age-specific information for cyclists
I'm over 50, starting my 30th year of cycling, and raced for 10 years when much younger. I've been tracking my performance over the 30 years with detailed training diaries. 

The main age related issue I've found is that it takes longer for me to recover from hard efforts. The consequence is that I cannot train as hard overall because I cannot handle as many hard days of training. I also find that I need to warm up longer before hard efforts, which reduces the time I can spend working hard in any given training session.

Overall, I haven't found much decrease in performance given the reduced amount of hard training. In other words, if I compare my current performance to earlier times when I was training at the same level of effort, my performance is only a little worse.

I'm curious to find out at what age I will start seeing a bigger decline.

I deal with the reduced number of hard sessions by pushing myself extremely hard during those sessions and taking it much easier on other rides. My goal is that my hard days are very hard and my easy days are very easy.