The reference point of the 1950s to the present is an anomaly because it's weirdly old in western culture, not weirdly young.
(2) The referenced article isn't really about marriage, but about the transition from adolescence to adulthood. There is a difference between a person getting married/ starting to have children versus setting up a household in which a person has an "adult" role; in the recent, Euro-derived West they are one and the same, but not so universally. And in the West, late age for marriage, and lots of non-married is the norm, and that pattern is pretty unique in the world.
If you do a graduate degree in demography, you learn all this. There isn't really any debate about it anymore, though it is very cool and interesting to discuss because it challenges our received knowledge about "normal". Don't get me started on fertility rates for women over 40 and their historical trends....
Among poor people in the US it is fairly common for a girl to have her first baby when she is 17 / 18/ 19 but still live at home; she has hardly left adolescence even if the boyfriend/ husband is also around...
Don't leave this hanging. At least point in the direction you're going.
The wikipedia article [1] doesn't agree with you. It suggests marriage in the mid twenties was most common, although there was regional variation. Noblewomen, such as the fictional Juliet, married younger.
[1] https://en.wikipedia.org/wiki/Western_European_marriage_patt...
I believe that "neolocal" households are unique, mostly, to post middle age Western Europe. And the 1950s are anomalous within that time scale.
Otherwise we see patri- or matri local multi generational households in which adulthood is not correlated with setting up a new household at all. You would marry someone and the move into their parents house. Sure you would start having children, but there isn't the same leaving adolescence thing.
Humans have a long period between when it's possible to get pregnant and when it's safest to get pregnant. This may suggest prehistoric females tended to wait around a decade after puberty, or there was huge selective pressure and we still ended up like this.