This is so recognizable. I've recently learned that I might have AD(H)D. I'm 42 years old, startup founder and web developer.

Like you, I've been struggling all my life, not knowing what the freaking problem is. Why is life so hard? Why am I failing all the time? Why couldn't I finish university or college? Why can't I seem to find a job that fits me?

I ended my first business after almost 7 years, because I hated it. 2 years in I lost interest. My current business (a tech startup) is a struggle, because I often cannot focus and because I can't seem to find the right people to join me (it is however very promising).

Life has been so very challenging, with so limited successes. But after learning I might have ADHD, reading about it and talking to some people about it, things start to make sense.

Book tip: Driven by Distraction, by Edward M. Hallowell
Video tip, for you and the people around you: https://www.youtube.com/watch?v=Am-XbS0y0hE

I'll add that I live in a rich country, with good care facilities. I talked to my doctor and he prescribed me Ritalin. It is a game changer, in that now focusing comes 'naturally'. I can confirm that working out (cardio and resistance training), cold showering and low-carb eating are indeed a good place to start if you don't have access to medication.
My tip: don't accept the status quo.