This only works for old women and young men. And, a young man could say it to an old man as a joke.
Any other way, the only response is "thank you."
I've always felt so uncomfortable about that joke. Like, both of us know you're old, me saying you're young almost seems insulting for some reason. I've never been able to put my finger on exactly why it makes me uncomfortable, maybe because it's just that it's an obvious lie even if it's meant to be "nice."
Now that I'm older, people just thank me, but when I was younger people - both men and women, especially older - would say something about how my parents raised me right.
I didn't really love that response, but I appreciated the sentiment and it never seemed inappropriate no matter the demographic of the complimenter.
Nah, old dudes can pull it off too as long as they aren't creepy about it.
Is this pretty privilege?
The only way I can imagine an old dude with a low charisma stat pulling this off is by giving the compliment while sprinting away at max speed.
he's just a kid, but he'll remember it always.