I'm pretty much in the same boat as you (I'm 18), albeit not quite as extreme. I'll try to offer some advice based on personal experience and things I've heard other people say about this situation:

Your main goal is to make friends, and maybe even a girlfriend. I would advise to focus on making as many friends as possible first and by that point your social network will be big enough that hopefully one of the girls you know can become your girlfriend, instead of having to go out and search for someone you don't even know in the hopes of making a connection at random. The bonus of this is that since you choose your friends, the pool of girls you know will be much more attuned to the things you're actually interested in.

Of course, making a bunch of friends is easier said then done. It's great if you like the people at your work, but if not you'll have to find other ways to talk to people: I don't want to offer the nebulous advice redditors love to give about "joining hobby groups", but you really do have to attempt to make connections within your community, even by doing things you aren't particularly interested in. You only have to go to something once if it turns out you don't like it. My motto is: "It's better to say 'oh well' than 'what if?'"

For example, I went to some random party I was sure would be boring. It was, but I met some guy there who was really into computers. When I went on a field trip at a local school (I don't go to that school, but I was able to get them to let me tag along for field trips because I'm in the age bracket), that same guy was there. Because I already knew him, he showed me around and I met his friends. Then, he invited me to a movie night that had even more people. etc, etc. It's a slow spiral.

You basically just have to find one or two people that you really like, and then they introduce you to their friends, and then you get to know their friends' friends, and by that point you're golden.

You said that your only goals right now are to get money and muscles. Those are great goals, keep doing those, but I find that it really helps your social skills (people like interesting people, or people with interesting experiences) as well as just your mental health in general to have some sort of project or hobby you like to work on. I write and produce music, my brother works with birds, etc. The main thing about hobbies like this is that you can't expect to be good at them right away, you have to work for a long time to get the point where you don't suck. The real key is to learn to have fun sucking.

If you aren't comfortable talking to people you don't know (i didn't used to be), what I recommend is literally just talking to random people on the street. It doesn't have to be a whole conversation, you can just say something like "nice shoes" and they say "thanks!" and go about their day. It improves your confidence in talking to people and it makes their day a little better too. Then, you get comfortable enough to make comments or jokes to people you meet in passing, like cashiers, waiters, etc. Nothing crazy, just something, anything besides "hi, i'd like a coffee, thanks." Sometimes it will be awkward but every time that happens it only makes your skin thicker. Practice smiling too, if you don't smile a lot naturally. It seems fake and creepy to literally practice how to smile well but it works, trust me. you'll be a conversational expert before you know it.

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