It is also nice to try to learn as an adult, but there are more limitations. I see it from my adult students. Usually, there is not a lot of time for studying, as life, work, family ask for their priorities. And that is pretty normal. As a child, your work is to study, although it is not always like that either hahaha 😂
You have made a super nice summary and added a bit more sense. Yes, yes, absolutely agree with this, networks that are not used become weaker, and when once it was strong and with a good base and memory, it can be reformed quickly! NOt so quickly everything, as I mentioned in some other comments, when something indeed very hard, technically hard, it is not easy to regain the same ability.
I somehow compare it now with athletes and achievements. The difference is what they can do when young and when older. I am afraid, even if I would practice again 4, 5, or 6 hours a day (as I used to do it 20 years ago) I think I would not be able to play again with the same ease the extremely hard compositions.
But, I should give it a try to know it 😂 Still not giving it too much hope as those hours for piano don't exist in the daily schedule 😆