Regardless, on your point about being diagnosed as an adult: I was diagnosed as having ADHD as an adult. It's not unheard of. The only reason I wasn't diagnosed as a teenager was that I wasn't hyperactive — just incredibly distractible — and I was smart enough that I performed "acceptably" in school. I've wondered, though, what I could have leveled-up to if I hadn't been fighting my distractibility.
Anyway, I was diagnosed at around age 30, was on meds (Wellbutrin) for about two years, and developed good skills and organizational techniques, so that I don't need the medication any longer. Ultimately, it wasn't the medication that taught me the skills; they just cleared my head and allowed me to develop them on the side.
If you genuinely think that you might have ADHD (specifically, ADHD-inattentive-type, like me), you'd do well to talk to a psychiatrist.