The balding greybeards are among the most respected engineers of my peers

But not necessarily when they apply for their next jobs, unfortunately

What?? Beards are discriminated against professionally?

Depends on the length of the beard.

Ah yea, that makes sense.

I knew a senior software engineer who was in his 60s, who was short, fat (pot bellied), completely bald (or shaven), and had a large white beard.

He also used to ruffle the feathers of HR. Once, when a woman from the talent acquisition team tried to give him generic instructions about conducting interviews, he told her “Lady, I don’t need all this, I’ve been doing this since before you were born”. (She was born in the mid-80s.) She reported him to HR, and obviously they didn’t do anything, since he was one of the most valuable engineers at the company.

He had a great breadth of knowledge and experience, and was really good at what he did.

So what you’re stating doesn’t necessarily always hold true.

Sometimes when people refuse to learn something new because they think they know better they are right, and sometimes they are wrong. Sadly it is difficult to know in which of these group you are, so it might be a good hedge not to refuse to listen to the young people. Even the most knowledgeable engineer can become a net negative quite easily.

Hubris right? Gets you twice, every time.