As someone who just turned 30, every year brings growth and change to my life. I'm not the same person I was at 17, or 24, or even 28. Every day I strive to better myself, or do better. Am I more set in my ways than I was 15 years ago? Maybe. But I don't really think so. I choose everyday to try to level up myself in some way, some days I succeed. But often I fail. And that's okay. Failure is a part of life - and an integral one. Struggling and failing is how you learn. It's also a cliche, but I find it to be true that success is all the sweeter when it comes after a series of failures. All you can do is pick up and try again. Because when you let failure stop you, that's the only way to ensure you'll never succeed.
You're young. You don't need to have accomplished anything at this point, you don't need to know what you want to accomplish later in life. Even if you never accomplish anything of note it won't make your life, or your happiness, less important or meaningful. Your goals don't have to be grand, as long as they matter to you.
Also I noticed specifically you mentioned sleeping around here. I'm not sure why you think sleeping around would hurt you in the future, or why you are beating yourself up so much over that specifically. But you should stop shaming yourself for it. "Sleeping around" is a perfectly normal part of life, at any age. As long as you're doing it safely, and with care for your own mental health. It's nothing to be ashamed of. It won't prohibit you from settling down in the future if that's what you want.
One of the things I realized becomming an adult is that no one has life figured out. We're all just fumbling around trying to do our best, whatever that means to us. Anyone that tells you otherwise is trying to sell you bullshit.
I definitely understand feeling like time is moving fast. It feels like just yesterday I was graduating high school myself. There isn't really much you can do about that except try to hold onto the moment when you're living in it. Not worrying so much about the past or future.
I think you should look into speaking with a therapist. You sound so overwhelmed and stressed out, and I think you could really benefit from talking to someone that isn't a faceless commentator on a website.