Arguably you are never too old for anything. However some people are intimidated by seemingly extreme fitness modalities like CrossFit at any age and especially over 50.
CrossFit can be a useful tool for anyone to get fit though. At CrossFit South Brooklyn, there is a special group of people over 55 who are doing really well as you can see in the video below. As long as your trainers are working with you to assess and improve mobility and form and not just beating you to death, you should be fine. And, of course always consult your doctor before any intense fitness regime. My trainer, Angelo Gala from EDX CrossFit in Lafayette, CO, also integrates yoga, kettlebells, endurance and other modalities to keep things fresh and allow me to recover from day to day.
If you want help and motivation to get and stay fit over fifty, join register for Boomerangfit by clicking HERE.