First off, I don't know your age, and it doesn't matter. Being an introvert, as I was when much younger, can be overcome. I still don't have a lot of close friends, but the ones I do have, I can count on.
You also didn't say whether your horse is on your property or boarded. If it's on your property, as others have said, social media may be one way to meet like minded individuals, but, also be careful. If you're boarding, You may have to step outside your comfort zone and introduce yourself to at least one of them. Just look for the one that seems most approachable.
You have gotten a lot of info and suggestions in this thread, keep alert, reach out a little, and be careful.
Horses do bring like minded people together, and age isn't a barrier, and they can help you to meet new friends.
Keep riding, asking questions, and learn how close we all can become.
Best of luck,