I mean, it's an insult, so it's a metaphor.

It's not literally saying, "you were born between 1946-1964."

It's saying, "you're old and out of touch, like the baby boomers."

I'm honestly not sure why people have such a hard time with this concept. They're basically the Skinner meme, "Am I out of touch? No, it's the kids who are the problem."

Which is exactly the point of the slang.

https://www.merriam-webster.com/slang/ok-boomer

There's a reason I specifically said, "as an insult."

The funny part is that by refusing to accept that the use of a word in a specific context has changed makes you a boomer per the slang definition.

Stop making me feel old, sir!

Exactly. Not to mention that "boomer" predates the baby boomers by a few decades. It was used for people in the boom towns during the gold rush.

It's an insult, so it's a metaphor. When you call someone a bitch, you're not calling them a female dog. When you call someone a bastard you're not accusing them of being born out of wedlock.

You're calling them the negative things associated with the noun.

Ok boomer

https://www.merriam-webster.com/dictionary/boomer