Asklemmy

I'd start looking at stuff like meetup.com, fun clubs in your area (climbing, gardening, aquariums, biking), and particularly singles adventure clubs. They are out there, and they are really fun. Not dating. Just making friends.

One night it will be swing dancing, the next week whitewater rafting. You get to choose what you like! They rented one of our chartered boats for a 4th of July out on the water when I used to bartend in college. Lots of cute men and women, generally 30s and 40s. They really seemed to be enjoying it :)

Meetup.com has events for a ton of different interests, I've found them to be quite diverse in age but some events are also focused for certain age ranges, so you might have some luck there!

Are you into bars at all? Finding a bar that already had regulars who are fun group is a pleasant way to make friends imo and you’ll meet people naturally once you know some people. All you have to do is scope out which one feels comfortable and visit at the same time each week. Obviously watch out for raging alcoholics, but lots of folks are healthy(ish) and just there for companionship.

Do they have to be in person?

This is pretty niche, but I'm in a casual curling league and nearly everyone is over 40. Everyone there is super welcoming and friendly.

I have a strategy where i'll get'em really hot by showing off all my 99s, but it's getting to that step that's been the hard part.