My experience as well. I was able to mask my ADHD with my high IQ, but I always felt like everyone else got a memo that I had missed, even when I was able to perform at a high level for short amounts of time.

Been diagnosed last year at age 42 and started taking medication. I think both quicker and faster because I don't get side-tracked and lost constantly. I can participate and even lead complicated discussions now when previously I would drift off because of something someone said that reminded me of something that has nothing to do with the discussion at hand.

If someone feels mentally sluggish it's worth looking into getting checked out.