Why is age often used to explain the inability to understand certain things?

For instance, I’ve seen so many memes about Baby Boomers not understanding technology because “that didn’t exist when I was your age”. Meanwhile, I’ve known Millennials who couldn’t figure out how to set up an iPad and I’ve seen people who were born in the Silent Generation that have figured out how to livestream.

In my opinion, age is not an excuse for not being able to understand something. I think a more reasonable thing to say would be “I’m not interested in that, so I’m not interested in understanding it”.