I think the reason for this is not only the obvious "young brains learn faster" but also different hormone levels, ego and so on. When you are younger, you over

I think the reason for this is not only the obvious "young brains learn faster" but also different hormone levels, ego and so on. When you are younger, you overestimate your skills and take on things that are actually above your level. Once you get older you start thinking more realistic about your skill-set and realize that other people are smart, too. You become better at estimating how much time a given task might take and you realize that you have other things to do. The problem is, you cannot grow if you do not push yourself to the next level. Practising something you already kind of know how to do will mainly optimize speed and avoiding mistakes and will let you plateau slightly above your current level. To really advance at something you have to take on tasks that are out of your comfort zone. You can then reapply the learned skills and concepts back to other areas. I think you have to actively massage your brain to prevent it from stagnating and freezing the algorithms it applies the most. It think we are blessed to work in a field that is conceptually challenging enough that we can actually observe this. In another area you would just wake up one day saying stuff old people say :D