I'm an American/Canadian millennial and I got married at 21. It'll be three years next month! I think wanting to wait to get married isn't really an "American" thing so much as a personal choice, influenced by individual culture.
For example, I live in Utah, where a large portion of the population is Mormon. A lot of people get married before the age of 23 here, and it's largely due to the fact that Mormon men are strongly advised to go abroad as missionaries for two years, and then find wives when they return. While they're gone, the girls find already returned boys and marry them.
I've seen people get engaged within three months of meeting. It's scary imho, and way more common here than you'd think. This is the only culture I've been exposed to growing up, though I know from stories my husband tells me (he's Chinese) that a lot of Asian parents want their kids to graduate university and then get married once they have jobs. But oh no, if you wait a few years, no one will want you anymore!
I don't get it, frankly lol
The whole idea that once you hit 30, you're suddenly that one left-behind avocado that got too ripe is, frankly, so silly.
LOVE DOESN'T HAVE AN EXPIRATION DATE