I'm not privy to any scientific studies on the subject you have raised although I am sure they exist somewhere. So all I can offer here at this point is my own experience:
I've had ADHD (predominantly inattentive type) since childhood, and BP2 since adolescence. Looking back from age 68 now, I would say that the ADHD has pretty well maintained the same level. Lately,however, additional symptoms are creeping in, and it is not easy to determine whether they are due to my advancing years or to an increase in attention deficit. I am referring to greater difficulty focusing on reading and listening. I also struggle now with remembering names, appointments, the content of conversations etc.
In regards to the latter and also to the reading issue, I would certainly blame an increased tendency for the mind to flutter off. The memory issues are probably more age-related.
There's no way one should generalize from one person's experience, of course. So it might be worth hunting around on the internet to see if there are any large-scale studies relevant to your question.
That helps. Thank you very much!