> “A younger-looking face creates impressions of higher physical and mental fitness,” the authors write. “Our results suggest that these impressions may indeed be a powerful driver of favorable employment outcomes.”

It is possible that there are other explanations. Older developers may want better salaries, better working conditions, be harder to manipulate, etc.

Good leadership is going to hire people that fits in the culture of the company and have the needed skills. Whenever the candidate is younger or older does not matter.

Bad leadership wants cheap employees that obey orders and don't challenge authority. Younger, more inexperienced developers will fit this category, even if they are technically skilled.

This is as good a theory that any other one to explain the fact that recruiters want younger developers.