I can really see your frustration. My daughter is 12 now and was diagnosed just about six months ago. As I’m researching symptoms and tips and remedies to help her I’m finding out I am showing or have had shown symptoms of ADHD. We as humans really don’t understand brain much and what was considered as bad behavior in past is now symptom of illness. Many people havent been diagnosed in past as we didn’t know much about it so it seems we are giving this diagnose just to anybody who asks. You must also consider that there is different stages same as with other illnesses like Autism, OCD, Diabetes, Arthritis …etc. You might have shown symptoms of much deeper case of ADHD than your friend of neighbor.
The only person who hopefully and rightfully knows is that person and his/her therapist.
So try to focus on other things than this frustration. Even that you thing you are done with school and getting help and/or trying therapeutic methods is pointless, don’t give up. You have long life ahead of you and it can still help you to improve in daily tasks, job….perhaps.
Best of luck to you 🙂