I did not write that older pilots were less competent than younger pilots. I wrote that it is harder to begin training as a pilot when one is older. There are plenty of scientific studies that support the theory that learning speed, developing new fine motor skills, memory, etc., decline from the early 40s. For example see Aging and Work in the 21st Century, Kenneth Shultz and Gary Adams (eds), page 231 which summarises the research in this area