The universality of marriage across time and cultures seems an empirical affirmation of the institution.

It supports propagation of the species, sure.

In the individual context of this thread, anecdotally, marriage is a forcing function that drives maturation.

Or not. Punt on the SO, and let one's humanity stay stunted.

Note that I am stipulating a non-abusive relationship here. Merely kids gaffing adulthood off.