I turn 40 in a few months. Is it still possible at this age to find a best friend?

[Coluber42]

I read somewhere (and this seems to jive with anecdotal experience) that close friendships are most likely to develop when you have frequent/regular contact with people that is basically required or automatic. So classmates and coworkers are likely candidates, because you see them all the time whether you make a particular plan to see them or not. Same is true for people at clubs, churches, gyms, buses/trains, or other activities you go to on a regular basis for some particular reason beyond just hanging out.
So that's why lots of people make best friends in college, for example. It helps that by college, your classmates are more likely to be people who share interests. I am still kind of sad that I really didn't make friends in college at all, because I know so many people who value their college friendships.
My spouse met his best friend in college, and they were roommates after; then all three of us lived together for about nine years until spouse's BFF moved out to live with his girlfriend. So at this point, spouse's BFF is basically my BFF too.
I've thought about this some recently because I've done only a mediocre job of keeping up with other friends and formerr coworkers; I mostly work alone now, and I miss having coworkers every day. I'm mostly too lazy or busy to go to social events, which I know is no one's fault but my own. But fortunately I have spouse, who really is my bestest friend. And our former housemate and his girlfriend live only five minutes away so we see them often.

But before I met Spouse, basically my entire social life was bicycling clubs. That's less true now, but I suppose that if I were in need of another social outlet, that's where I'd retreat to.