Most studies show that mental abilities continue to improve to at least 40 years old, if not later. You can see this in the chess masters. After 40, the effort required to beat the young pups does start to take its toll. In general however, after 40, then experience will let one coast, and run circles around the young pups coming up. The reason here is that we are talking about a product with no physical attributes. Hence, I don’t buy the age thing at all.
However, what I do buy is that things are a good deal more difficult today, then say 15 years ago. I used to know all of kinds of dbaseII/FoxPro developers back then (I was one too…but I also went to University and took computing science). It was real easy back then. Just design some files, and write some code. As soon as some server type software started being used, most of the dbaseX developers quit this profession, and moved on. In fact, a good many stopped when windows came along. Today for commercial applications you need to know sql,, sql-server, ADO record set objects etc etc. In other words, today you need to know *way* more, and have to master *way* more complicated technologies just to write software for a average business. In fact, you need to know more in general just to accomplish a simple task. Those dbaseII programmers did not have the ability, or did not want to make the effort to start learning new environments that were more complex. Fact is, that every 3, or 4 years you have to learn a new development environment. I guess some get comfortable with their current environment, and don’t have the desire to move on to the next environment. When that happens, it is time to leave.