Yes, but ADHD is much more than just not being able to sit still all day. There are working memory problems, time management problems and much much more. It affects interpersonal relationships, job performance and many other parts of a person's life.
As a person with ADHD-Hyperactive-Impulsive type grows up, he will start showing less and less hyperactivity (the impulsivity is still there though).
The problem is that the number of children being diagnosed with ADHD seems dubious(I accept that there's real cases). According to the stats in[1] 20% of boys aged between 14-17 have been diagnosed at some point with ADHD. When you're diagnosing 20% of the male population with a condition isn't it time to accept that it isn't a condition, rather it's within the normal range of behaviour (many of the symptoms would be simply be considered an aspect of one's personality in other times).
As a person with ADHD-Hyperactive-Impulsive type grows up, he will start showing less and less hyperactivity (the impulsivity is still there though).