Honestly, I think meeting people at 38 is really hard. Especially if your social skills are somewhat rusty.
I think a lof of the advice is well-thinking, but it's not very good as things aren't that easy.
I believe that the easiest is to get into something geeky, but not competitive. Maybe it's 3D printing, or treasure hunting, or setting up fish tanks, or board game design, or fan fiction writing, or cosplaying, these kinds of stuff. If it can be physical, it's good. Like, bouldering is fairly geeky. It's also very hard if you're on the heavy side.
I think the geeky competitive hobbies are not good. Like chess is not great to meet people, as you'll need a lot of time to build up the skill required to even talk to someone without sounding dumb.
You need something that:
1. You can spend long periods of time doing on your own.
2. Has a strong ONLINE community (it's a lot easier to get into online stuff)
3. Allows to occasionally meet up in person.
The main thing is that geeks are nice people. They are way more welcoming than the average couple who's usually tangled in kids' education, paying the mortgage back, seeing their friends and family. And you can meet people online, which in itself is social contact that's good for you.
If I was in your shoes, my plan would be:
- try geek stuff that requires some advice. More ideas: clay sculpting, jewelry making, woodworking, and find one that I like.
- seek online communities and chat to people there. This would allow me to build up my skills, show off my stuff, get feedback, and start creating friendships. I wouldn't worry about being online too much at this stage. I think I'd try to find different coomunication channels, like IRC and discord. I don't know if things like second life are still a thing, but this used to be good too.
- Become "someone" in these communities. Like people know who you are. At some point people don't talk about the hobby, but conversation easily go more intimate.
- Meet people up when you can.
On top of meeting people, this has a great benefit: you have something to talk about to other people.
Like if you get into treasure hunting (like I did for a while), it's a great conversation starter. People think you're a bit crazy, but they love to hear that you went in the woods with your pickaxe and your shovel.
Anyways, I know that's what I'd do.
Good luck