As Glen mentions below, it does seem that people become less flexible as they get older. One reason might be Bayesian updating. An alternate reason is that often skills are specific to a certain task or way of doing things, and each new skill is costly to acquire. Most people have made a substantial investment learning to do things one way. If a better way comes along, it may be optimal to stick with the old not-quite-as-good way and not pay the cost of learning something new. A young person faces the same cost (learning to do it) either way, and so might as well pick the new way.
Magnifying this effect is that the benefits of learning something new are lower the older you get. There is less time to get a payoff from new knowledge. Why learn the latest computer software for your job when retirement is three years away?
This is one reason that intellectual revolutions are often led by the young. Older scholars have skills invested in the established paradigm which gives them an advantage as long as that paradigm is dominant. They understand it better and are better at applying it. Furthermore, they would have to learn a new way of thinking about things, and why learn the latest theory when retirement is three years away?