To OP, I feel your pain. A little back round-my DW and I (both also introverts) met our $ number many years ago. We both feel like we're not even close to pulling the trigger as far as lifestyle. I am a business owner (56), she is a second grade teacher (55), and we love what we do, which is fine. Also it helps that she has the summer off and I take a lot of time in the summer. We have a house and boat at the Jersey shore that we get to enjoy almost every weekend. I agree with the above posts regarding making friends at an older age. Now that the kids are grown we have less chance of meeting new people. Of course I think we can all agree the generic "stay active/have a purpose" are important when retiring. I wanted to post some of the specifics of our transition plan in the hope there may be a nugget in there for you. Important to note we have already started most of these efforts!
Community Involvement.
Serve on our local hospital foundation board. I've been doing this for years, tons of opportunities to fund raise in order to buy the latest gizmo or help those who are less fortunate. Also meet and work with some really neat people.
Join our local fishing club. We get to hang with people who want to talk about boats and fishing all day!
Help with events at our local church.
When I FIRE I will join the local fire dept. Not to kick down doors and climb ladders but more to help with whatever they need, direct traffic, drive, man the griddle for the pancake fundraiser, etc.
Get involved at our local college. Again, a lot of events whether it is sports, theater, fundraising. Sometimes we are guests, sometimes we are volunteering. Being around the students is always fun.
All of the above you can get as involved (or not) as you prefer. BUT, my experience has been you only get out what you put in...
Friends:
I have a bud who sold his company and RE about 10 years ago. His mindset is you need to make new friends while keeping the friends you have. He has different groups of friends for different interests. My DW and I are doing this now.
Country concerts. We do 6-7 each year, going to see Kenny Chesney in Nashville in June.
Travel. We did 10 days in Costa Rica with adventurous friends (zipline, WW rafting, racing UTV through the jungle). Another set of friends like history/food/ghost tours so we did a week in Ireland. Another group loves skiing. Another group loves SCUBA. This could be endless.
Game night, regular meet ups with 5 other couples plus we do 4 murder mystery dinners each year. The best costume gets to keep a little plastic trophy until the next dinner.
Wine club. Yet another group loves to meet up every month or two for a wine tasting party. As the host location changes you get to meet friends of your friends and BAM more wine and talk of travel, games, concerts, etc. It's not uncommon to break out the credits cards and book something before the night is over (Notre Dame/Clemson in November the latest addition).
And so I'm full of courage right now but I haven't actually jumped into the RE pool yet. Maybe I'll feel differently when the time comes, who knows?