[Chuck Kennedy]

Those are the age ranges used for the Senior Games for competitors over 50. I did a study that pros lose 1 throw (10 rating points) every 5 years on average starting at age 40. But I'm not sure that's enough to justify 5 year ranges until perhaps 60-65 where we didn't have enough data to see if it was still 1 shot lost per 5 years. It appeared to accelerate.