ADHD is a spectrum disorder. There is no bright line where an ADHD person exists and non ADHD people exist. You can't measure this bright line with "symptoms"
Thus the DSM and other doctors measure the line based off impairments in daily life. That said impairments are something that the environmental effects. Thus you may have ADHD since birth, but only become impaired when you went off to college, for until then you were still prospering under the eyes of your parents and teachers. You may have struggled but you were not "impaired."
Furthermore while ADHD is a spectrum disorder and often you see ADHD symptoms in a family where it is part of the family phenotype some of the family members "may be impaired" by their symptoms while other people are "not" for they have enough other non ADHD behaviors to compensate. These other non ADHD factors can be "neuroprotective" so while you may have ADHD symptoms like poor working memory, you are not impaired in daily life for you have enough other things to compensate for the working memory.
Dr. Barkley calls that 5 minute speech ADHD vs a sparkling personality (where you may have ADHD symptoms but are not impaired by these symptoms.)
A disorder is a disability. Symptoms != disorder, disability, or impairment. Scoring bad on a working memory tests or wisconsin card sort does not mean squat in real life whether you are impaired in daily life activities. These tests and rating scales are only meant to make it easier to find the ADHD people who are suffering impairments and get them treatment as soon as possible so you can lessen the severity of these impairments. If you are not impaired you do not need external treatment but if you are on the border of being clinical vs subclinical you probably could learn some things based off the non med treatments for ADHD.