> But in big companies (Amazon, Google, Twitter) in enterprise software companies, banks, medical tech, finance, I think it's not that uncommon to find 40 year old developers.

I think there's a bit of survivor bias. More interesting are the stories of someone who's not at one of those large or old-school companies. There's a bunch of skills (MFC, Flash, microcontrollers) that used to define 95% of someone's job, and are no longer relevant.