It is a fairly recent thing for ADHD to be diagnosed in adults. In children, more males than females tend to be getting diagnosed. The gender imbalance in diagnosis is thought to be due to how ADHD presents in females - as an inattentive rather than a hyperactive type (you can have one or other, or combined type).
The research into adult ADHD presentation, effects and therapies is still emerging. In recent years, a range of personal bloggers, coaches and YouTubers have helped significantly increase awareness and understanding too, through sharing experiences of their own personal journeys or experiences of the condition. I enjoyed this article from Leanne Maskell (ADHD Coach and author of ADHD: an A to Z), writing for the of association of MBAs, where she explains how ADHD may show up at work.