[swatcoder]

I think a bigger “legitimate” factor is craft culture.

Because of the industry’s recent rapid growth wave, the approach experienced older developers take to the craft is often very different than what’s trendy among younger developers and teams where they dominate, and there’s easily a clash where both think the others’ approach is totally bonkers and a red flag.

Somebody seeking a job may know or believe they can adapt, but the hiring team just sees an outsider and assumes the outsider doesn’t know how to do things “right”.

This applies to skilled young developers trying to break into “old school” teams in defense/enterprise/industrial/etc as much as to older developers trying to keep up with youth-dominated FAANG and imitators, but it’s tolerated in the former but can get labelled as ageism in the latter.