Although many people may feel like they have some similar symptoms, genetics play an important role in ADHD and a full diagnosis is given to those who are negatively affected on a daily basis.
Pegg said he had previously been putting his symptoms down to “just character fault”.
The actor and writer also spoke about his mental health, including having clinical depression and struggling to control his drinking, which he said he initially thought had “caused” his diagnosis.
“I felt like it was something that had come on in later life because I wasn’t a naughty child.
“I’ve had bouts of depression in my adult life since 18 and I thought maybe it had come on with that.
“Maybe over the years with therapy and medication – whatever – I’ve been treating the symptoms and not the cause of why I feel that way.”
Pegg said: “I did feel different in a way I might not be able to put my finger on. Maybe everybody feels that way.
“I just assumed ADHD kids were kind of chaotic and difficult and didn’t pay attention in school,” he added.
“But there were other things that I did do as a kid – fidget or whatever – that made me think, ‘Oh no, maybe I’ve had this longer than I thought’.”
Pegg said his wife has been supportive and is “dealing with it as if I’d been diagnosed ages ago”, adding: “It’s just who I am, and it’s just things that I do.
“She makes allowances for forgetfulness and and lack of concentration.”