Anywhere alcohol is involved.
If you were female, it might very well be. 
Of course one’s personal circumstances vary, but my guess is that for most people, college (or school in general) represents the most easily accessible potential dating pool of people. I dated much more after college, but there were far more options available to me during college.
If you’re a single male and not anti-religious, church. Single women everywhere, of every age. And not necessarily bible thumping Jesus freaks, especially if you go to a more liberal denomination. My Episcopal church has plenty of attractive single non-crazy women between 25 and 40.
My wife and I were set up by my roommate’s college buddy’s wife and sister. Wait, I mean, his wife, and also his sister, worked together to set us up. Not that he married his sister.
I don’t know how dating works, now or in the past.
Waaaay back in the past Zog would just club his, um, selection and drag her off by the hair.
Let’s see: met girls in high school and college, of course, including some with whom things only became interesting years later. Met a couple of women through college friends after graduation, met a couple of women, including my wife, in grad school, even though I was studying mathematics. One girl I dated was a friend of my sister, another I met through caving buddies, another at a retreat for volunteers at a crisis hotline, a few through personals ads in alternative weeklies, and a couple through chance meetings: one time I got in a really good conversation with the woman behind me in the checkout line at a store, and another time I was in a restaurant with some friends, saw an attractive woman at the next table, and sent her a dessert.
All of this was pre-1990, so very very pre-Internet.
Funny thing, I was the chef at a major night spot in San Diego in th 1980’s. Cocaine in the bathrooms, dirty-dancing, nudity in the photo booth, high-priced drinks, cover charge, gorgeous lady customers and co-workers.
But I never got laid.
anyone remember Confetti ?