I think the stretching stuff is done by people who like pain with their sex but who knows. I've never been a fan of it but it isn't a millennials thing. Previous generations did this and tattoos out the wazoo. Millennials are just the generational whipping post, blamed for everything. If the hole is small enough it grows back together a lot more than you'd think, I've seen small holes grow back into just a normal piercing. If you get a big hole you end up with droopy holes that look like melty skin ear rings. The holes shrink either way.
I've never been interested in piercing at all.