I don't know if it's about being young and undisciplined, possibly due to inexperience. It takes time to learn business and time planning and how to stop being impulsive when the next big idea comes up. I strongly disapprove of people becoming entrepreneurs with zero work experience. There are always exceptions, but in general it is good to learn from the mistakes and experiences of others.
You have undiagnosed ADHD, and medications will help you focus on business and planning how long you're doing, but don't get attached. There's all this that comes from ADHD or that adults don't need medication, blah blah. I've heard crap from parents who should know better.
What I'm also seeing are the adults who have struggled with what you suddenly describe and find that they have the ability to see things, choose a path, and follow it despite tempting alternatives. My friends are being diagnosed at 50 years old. My children were diagnosed at age 19 and 21 because good kids don't raise red flags in the New Zealand education system, but they fall apart when they try to "grow up" because that shit is hard. You are in the United States (I think) and I suspect they are not very different.
FWIW the advantage of ADHD is "hyperfocus" and that is a powerful tool. It allows you to be completely immersed in a project and oblivious to the time it flies by. First responders often have ADHD because they can give everything to a situation when they need it with better results than NeuroTypicals. Programmers do it well because we don't go from A to B to C, we can see Z from here and all the intermediate steps very clearly.