Correct, but people are more likely to learn a new skill or a tech stack in their 20s than in their 40s. And when current 65+s were in their 20s javascript wasn't a thing yet.
Not sure people over 40 don't want to learn new things; they're likely just more interested in stable long-term technologies and investing their time wisely rather than hopping onto the newest fad all the time. With age comes understanding that the more things change, the more they stay the same. Emperor's new clothes and all that.