Young adults have many of the same symptoms of Attention deficit hyperactivity disorder as children. Some may experience different symptoms to a greater or lesser degree, while others may have different symptoms entirely. This article provides an overview of the symptoms of ADHD in young adults.
Hyperactivity or “Feeling Restless”
Among the symptoms of ADHD in young adults are feelings of hyperactivity, which are expressed as “feeling restless." In addition, the hyperactive young adult finds it difficult to complete quiet activities that require sitting still. When required to sit quietly at a desk at work for example, some young adults may bounce their knee or tap a pencil on the desk repeatedly, trying to work off some of the nervous energy building up. 
Young adults with ADHD who suffer from inattention find this symptom negatively impacting school, work and social situations. One way this might happen is when a young adult is with friends. The friends might be talking about or doing something and the young adult with ADHD temporarily “zones out." When attention returns to his or her friends, a significant chunk of what has just taken place has been missed.
The routine daily tasks, while they may be simple to carry out, cause problems for the young adult with ADHD. Transitory or irrelevant sounds and sights cause distraction. The young adult moves quickly from one activity to another, getting easily bored with each one. At work or in college classes, this particular symptom causes problems with supervisors and professors, as the young adult misses details, misplaces assignments or projects or turns in work that is incomplete.
This particular symptom causes interpersonal problems because the young adult has such poor listening skills. When others bring up a conversation or give instructions to the young adult, he or she has a hard time remembering and following directions. 
It is ironic that a disorder that makes it difficult for the young adult with ADHD to pay attention also causes the same person to develop a “hyperfocus" on enjoyable and rewarding activities.
Hyperfocus is a coping mechanism for distraction. The young person becomes very skilled at tuning out extraneous “chaos," such as finishing dishes or the accounting assignment gathering dust in the book bag. When the young person is able to develop a hyperfocus on productive activities, it can be beneficial, but if it is not addressed in other areas, relationship and work problems can be the result. 
The house, desk, office and bedroom of the young person with ADHD reflects the inner person. The different home, school and work environments are cluttered, messy and scattered with papers, books, dirty clothing, lost keys, small piles of change and possibly a gaming CD tossed in for good measure. The young person with ADHD literally cannot exercise the necessary executive function and organize everything that needs organizing.
The result is someone who is always late to school and work appointments, forgets deadlines, doesn't finish projects, loses items, and has chronic procrastination. 
The young person with ADHD speaks and acts before thinking. It is difficult to hold back behaviors and comments such as, “Wow, you gained some weight — or are you pregnant?" to a friend. Obviously, some of these actions or comments are hurtful, which harms interpersonal relationships.
The young person also interrupts others, talking over them as if unable to hear them talking. What is happening here is that the ADHD person wants to say what he or she is thinking before forgetting it and the thought is gone, probably forever.
Some young people with ADHD act recklessly, as if they have not thought about any possible consequences. Other young people develop addictive tendencies — gambling, alcohol, illicit drugs. 
Finally, among the symptoms of ADHD in young adults, emotional issues are seen more frequently because they have struggled lifelong with feeling and acting different.
Some may not handle frustration well, blowing up unexpectedly. Others struggle with low self-esteem, feeling a sense of underachievement. Then there are those who get stressed and flustered easily, and are not able to handle difficult situations easily. Young people with ADHD may experience mood swings and irritability, have trouble with motivation, have short tempers, be hypersensitive to criticism and feel insecure. 
 Attention-Deficit/Hyperactivity Disorder: Symptoms of ADHD. WebMD. Sept. 2008, retrieved at https://www.webmd.com/add-adhd/guide/adhd-symptoms
 Melinda Smith, M.A. and Jocelyn Block, M.A. Adult ADD/ADHD: Signs, Symptoms, Effects, and Treatment. Help Guide, retrieved at https://helpguide.org/mental/adhd_add_adult_symptoms.htm