You may or may not have some ADHD tendencies, but it’s not uncommon for people to miss out on diagnosis as children.
I wasn't diagnosed until I was 19 or 20 because my perfectionism (which was/is directly tied to the anxiety/major depression I was diagnosed with at 14, but self-diagnosed at 9) sort of overrode the traditional symptoms. I did well in school (because I couldn’t NOT have perfect grades). I excelled at work. For many years, I was compulsively neat. (I’m not really sure what happened to the neatness).
When I was 17, I was put on ADHD meds as a way to treat side-effects of an antidepressant, but I found it had a ridiculously positive impact on my life. In college, I was formally diagnosed, and my psychiatrist posits that the fact that I appeared to be “fine” is what kept me under the radar. According to my doctor, it’s not uncommon for that to happen, especially if the individual is of above-average intelligence (I was given the “gifted” label before entering kindergarten).
I always “joke” (except, it’s not a joke an I’m 100% serious), that I’m a high-functioning ADHD person. And it’s true; over the last 15 years or so, I’ve learned to augment my behavior and recognize when the disease is impeding on my life. For clarification: being able to recognize something != always being able to change what is happening. I’ve also been fortunate to find work in fields where my ability to do multiple things at once is useful.
But I tell people I’m in meetings with frequently about the stuff I do to help quell my worst tendencies (I play puzzle games on my phone, for instance, so that I can pay attention to what people are saying. It looks rude, but the alternative is me literally not being able to focus on what is being said. And when I explain it, I’ve never found someone to be unsupportive), and I try to plan and make adjustments for my own time clock.
Like you, if it’s something I’m interested in, I can be hyper focused for hours. But the second something is born for even just not that compelling, it’s a struggle.