From where I sit, I can't figure out if this is a real thing or just hype. I'm 45, and had exactly zero trouble switching jobs recently, becoming employee #15 (developer #5) at a startup that just did its A-round. They said they liked the fact that I had done a bunch of different stuff, including founding a company in the 90's, and that I had an obvious passion for what they were doing. So, I'm not (yet) freaking out about the bits of gray in my beard.