How to get back..?

I’m 27. I haven’t dated since sophomore year in high school (roughly 12 years ago). After my high school relationship, I realized that high school dating was useless and decided to just focus in school. After I graduated I continued on with that mindset and basically turned myself from an outgoing and talkative person to just a very very introverted and closed space person. Turning 27 recently, I realized a lot of people around me are getting married, starting families, and etc etc. I’m not getting and younger. But I for some reason still feel like I’m not ready to date. I tried dating in college. Went on a few dates. But it didn’t feel right. The girls I talked to were friends at first. We clicked as friends. But then when it came to a date, they put their guards up and it ends up being a quiet and awkward date. I shut myself down after that again and just focused on graduating college. Is dating a decision? Or does it just come naturally? And how do you know if your ready? I sound desperate. But I don’t think I am either. I’m not no Ted Mosby. But my end goal is the same as him I think. Meet the one and get married and start a family. But I don’t see marriage in my future. And I can’t see dating in it either. Am I just one of those people who wants to be alone? Could use some advice. I think I’m just over thinking this out.