I agree with much of what others say: if you want to assess your mental ability, first count how many other tasks/responsibilities/distractions/obligations etc,

I agree with much of what others say: if you want to assess your mental ability, first count how many other tasks/responsibilities/distractions/obligations etc, you have in your life. When I was young, to a large extent I could concentrate on the task. And I ran. Later with two kids, a dysfunctional wife and dysfunctional job - not so much. I'm over 65 now. I still like programming. I have lost some quickness in some kind of memory, but that is made up for by a much, much deeper understanding of the patterns. I'm not sure how to describe it. And thinking of patterns, perhaps that is part of what you are up against. I find that trash code is increasingly hard to sort through. Does the API itself make sense? If not, then maybe you are better off thinking about how it should be written. As a starting point.