I've got diagnosed at age 26, now 16 years ago. This was after a whole set of tests, spread over days with observation included. You need a professional because there is so much involved.
Everybody's different so even though articles and YouTube videos on the subject may seem recognisable, sometimes they also describe stuff that I don't experience.
There is no hyperactivity on the surface but that doesn't mean there is no hyperactivity at all. I for an instance became very well at hiding and suppressing the 'H' in ADHD. So much that even to me it seems like there's nothing there.
So, get tested by a professional. When' you get diagnosed, see how that can work for you. I for an instance had poor results in high school but graduated magna cum laude in law school four years ago.
Being diagnosed made me look for alternative ways of organising my life and made me more successful. At least it made me understand myself.
I never knew. Wild story.
Apparently:
This is all new to me.