Here are the reasons why;
1. It is quite stressful - old traders will soon give up due to mental health problems
2. It is not enjoyable anymore - nobody will stay long in a job that they no longer find themselves comfortable with especially if you are not earning well.
Most of the time we feel this during bear season.
3. Trust issue due to Scam growth - traders never find it safe to use exchanges, even big exchanges.
I differ completely from your perspective, once we grow older we just want to enjoy and trading can be one of the way to make money for an individual at their comfort. I am not talking about the day trading but longer formats is quite convenient and anyone who has decent capital can do it with less risky plans and make money for their needs.
Because I would agree that trading is stressful and I don't think we should stress ourselves if we are old already. If we think for pastime, I don't think this is a good decision. We better just invest and leave peacefully live without thinking about the market situation and do research because we trade. Why not just sit down and relax, and wait for our investment to grow rather than stressing ourselves to check always the market price?