I got married in 1990 aged 21, my husband, who's actually still my husband, was 22. Neither of us had just graduated because neither of us were at, or intended to go to, university. We lived together for six months before we tied the knot. I don't remember anything about it being frowned upon.
Why? Because we wanted to. I mean we loved each other, still love each other, and we were realists. We didn't have this idea that we would independently sort out our life and future and then meet someone else who had also entirely independently sorted out their life and future. Where's the fun in that? We wanted to do it together. And we knew it would be a bit up and down / thick and thin, etc. But I would say that we'd both been working since the age of 16 and we'd both already left home by the time we were 18 and weren't dependent on parents or anything. Like, we'd been adulting for a while, doing the 9-5, paying all our own bills, etc.
Anyway, yeah, we made it. We did go to university in the end. He was at it for a long time, got a PhD, became a lecturer and I'm a teacher.
Now we're both approaching 60, it's funny looking at our shared past that doesn't involve any other partners. The marriage is sort of baggage free in that respect.