And if a company is using a popular language/framework they can find senior developers who know the language and the stack. Why should they hire someone who hasn’t taken the time to learn both?

That ramp-up time being significantly shorter for a senior dev is what we're talking about, and how selecting for the specific stack like you're describing isn't necessarily going to be worthwhile - learning the domain is likely to take longer than learning the technology.

Not really. If someone has ever been exposed to a similar framework - take your typical MV* framework for example - even a developer whose only been active for three years can easily transition.

I have no idea why old folks (putting myself in that category) think they can get by without keeping up. Do you really think that someone who has 15 years of experience but haven’t kept up with the industry won’t be at a disadvantage over someone with 5 that has? On the other end, you have people like me that knows what it’s like being behind the curve and vowed never to put myself in that situation again.

You can’t imagine how long it took me to unteach a 50 year old who had been doing ASP.Net web forms for years how to even develop in ASP.Net MVC using server side rendering let alone client side frameworks.

He was only eighg years older than I was but didn’t keep current