[RAdrien]

Popular accounts from earlier decades, when fewer people went off to college, suggest that high school used to play this role, as well as being a place where many people met their spouse.

My guess is college itself is less important to lifetime friend accumulation than spending any amount of significant time with age peers when you’re a young adult. In my circle, many life-long friendships were formed by young colleagues in their first jobs or among young post-college roommates.

The typical college years just happen to line up neatly with the part of adult life in which people are most interested in new experiences and new people. You tend to make lots of lasting friendships when you’re interested in making friends, and everyone around you is as interested as you are. As an older adult, most people in the same stage of life simply have no interest in friendship with you.

[jorl17]

While that certainly plays a part, I think it's also the fact that in several colleges you work as a group in the face of adversity. At least it was in my case.

We formed a group of very close friends who all worked together "against the system" to get the best grades possible while somehow staying sane[1]. Long days and nights working together, or just shooting the shit _at college_ because we were bound to stay there working.

I'm 100% sure that in my personal case, I would not share the bond I do with my friends (even if they were other friends) if I had not met them under these circumstances.

[1] I have been extremely lucky to have belonged to a group of "top of the class students" who worked together, shared notes, assignments and helped each other, instead of competing and throwing each other under the bus -- I know of other people who did not have the same luck.

[jeffbee]

Just my personal anecdote: while I still have friends from high school and college, some of whom are important friends to me, my colleagues from my first year of professional work have been life-long companions who come and go regularly, some as repeat colleagues, some as casual acquaintances and some as close friends. You may share certain things with a person at college but sharing a 30+ year career path with someone is also fairly significant.