Here's my experience with an elderly coder in his mid 50s. He was a decent delphi and .net coder, he was a decent human being, but he had health problems. Most of the week he had hospital appointments. He required nose surgery. His blood levels were low. He needed vitamin d and iron supplements and during our four month acquintance, he never got any better. He constantly forgot things and he feared his lack of iron had caused a permanent damage to his brain. He was a diabetic which gave him license to be more hot headed and harder to persuade. He had accumulated a lot of debts which gave him license to be more hectic and disturbed. Overall, his long life and experience did not outweigh his negative properties.
I hate to tell you this but you're looking in the mirror at your future self (and your peers) as coding isn't usually in most cases a healthy lifestyle choice.
That may be true, but it leaves me with the frustration of having no other choice as I haven't developed interest on any other subject that would possibly give me a more healthy lifestyle. Perhaps being rich with no worries in the world would help?
So you met one guy with a lot of chronic health problems and assume that everyone else in his age group is similar?
Or if not then I'm not sure what your point is. People who miss a lot of work and make excuses for being belligerent don't make the greatest employees, but there's not as much correlation as you think between that and age.
I feel like you really have given a clear answer to combatentropy's question "why do employers discriminate against older people", but it's maybe not the answer you thought you were giving.