As to staying sharp: I used to think I used to learn really easily.
But then I did some digging and found that in general it took me always at least 3 tries to master some new subject.
The first a brush up, look at and small understanding.
The second when having to do something in or with it and a slightly deeper understanding.
The third when the coin finally drops and I felt that I had mastered the subject.
Between the three phases there can be arbitrarily long breaks.
When I was young and had few responsibilities it would not take long to get through these three phases because I simply had little else to do.
Now that I'm older and have a fair bit of other stuff on my plate I find that the 'breaks' in between last longer. But the actual learning does not, in fact if anything it goes faster.
So all this may simply be due to an illusion, where 'wall time' vs 'process time' are further apart than they used to be and you're measuring by 'wall time'.
You're probably every bit as sharp if not sharper than you used to be, but you perceive it to be otherwise.
As to staying sharp: I used to think I used to learn really easily.
But then I did some digging and found that in general it took me always at least 3 tries to master some new subject.
The first a brush up, look at and small understanding.
The second when having to do something in or with it and a slightly deeper understanding.
The third when the coin finally drops and I felt that I had mastered the subject.
Between the three phases there can be arbitrarily long breaks.
When I was young and had few responsibilities it would not take long to get through these three phases because I simply had little else to do.
Now that I'm older and have a fair bit of other stuff on my plate I find that the 'breaks' in between last longer. But the actual learning does not, in fact if anything it goes faster.
So all this may simply be due to an illusion, where 'wall time' vs 'process time' are further apart than they used to be and you're measuring by 'wall time'.
You're probably every bit as sharp if not sharper than you used to be, but you perceive it to be otherwise.