Yes, they do. The presentation of ADHD in a six-year-old is much different than in an adolescent or adult. The symptoms are very similar, but their manifestation changes with age.
A small child may present ADHD through behavior such as extreme hyperactivity, inattentiveness, and impulsivity. All small children exhibit these characteristics now and then— they’re part of growing up—but a child with ADHD will be like that every waking moment.
An adolescent with ADHD will present the syndrome in a much different way. He may do very poorly in school despite obvious intelligence, have a tendency to “zone out” during class or while his parents are talking to him, be moody or irritable and exhibit serious behavior problems that result in few friends. Again, a great many teenagers are moody, irritable, and difficult to be around—but not all the time. Nor do most normal adolescents present such a neat package of telltale symptoms.
ADHD is a bit trickier to see in an adult, though the symptoms are similar. He may have trouble focusing on and finishing projects at work, experience difficulty relating to bosses and co-workers, be irritable and moody at home, and have problems with interpersonal relationships because of his temper and inability to focus.