Here something else that I forgot to mention: I wish I had put in the work to plan my social life earlier.
In my late 30s, I started spending 2-4 hours a week on learning what's up in my city. I live in Washington DC, so I got a subscription to the local magazine, The Washingtonian. I read the free culture weekly newspaper, The City Paper. I signed up for a blog called freeindc. Later, I added researching eventbrite and reading Time Out.
If you live in a major city, I strongly suggest that you sign up for your city's magazine, you will be shocked by all the stuff going on in your city. One of the best $15 investments you can make.
Now, I know all of the best happy hours, best rooftop bars, all of the live music spots, art events, festivals, and cool stuff going on in DC. This work has made my life way more enjoyable. I keep lists on my phone of all the interesting things, and place the events on my calendar so I don't forget about them.
The other thing I wish I learned earlier is that you really have to try something before you know if you don't like it. Being broad minded and curious has led me to do some things I never thought I would do.
Stretch out of your comfort zone. Go try new foods; listen to different music. I realized that I can enjoy genres of music that aren't my favorite live.
With all of the research that I do, I probably only get to 10-20% of the stuff I want to try. But, I have a great social life because I put in the work.
Chicks that go out with me know that they have no idea how this night is going to flow because we are going to be in some spots they never knew existed.