It does not surprise me that the research is in conflict.<p>It makes sense that as programmers age they either become better programmers (through experience) OR they stop programming (the bad programmers flux out of the field with time). These two factors combined will tend to make older programmers as a group look better than younger ones. <p>But there are hypothetical factors that can work against older programmers as well. For example, if the older programmer has not bothered to keep learning new things he will be locked into one domain where his expert skills are useful. This will cause trouble if he ever needs to work on different types of systems.