I don’t think that ADHD “gets better” when people grow up. I think that life and circumstances change, and change affects ADHD. But this is a problem with neurodevelopment and brain chemistry, it doesn’t magically go away.

That being said, it sounds to me like you might not be medicated. That’s ok, if that’s your choice, but know that medication is the single most effective treatment for ADHD that exists right now. On its own, it’s not enough, but without it, shit gets real. Dr. Barkley has some great informative videos that really help to explain how ADHD works in our brains, and the role of medication. So. In that regard, I suggest you reach out to your doctor.

Smaller things that might help though, I always find that if I really need to concentrate, or if I really need to get something done, voices distract me (podcasts, videos, anything where someone is talking). So, I will listen to music instead, particularly music without lyrics. Lo-fi works well for this for me, or piano music, or whatever. I just try to keep the lyrics (voices) to a minimum, and it seems to help.

Something else that helps when I really need to focus is a fidget toy in one hand (give your mind monkey a banana) while I read/learn/concentrate. It’s such a small thing, but it helps SO MUCH!

Good luck, hopefully these work for you!