Ask HN: I'm 40 and feel my mental ability declining. Programming seems harder. 4 years ago
I discovered that if someone tries to do something that has abstractions and multiple branches (not in a Git way) and tries to put everything in his head -- will be fail. So my solution for that cases is: take notes, create flow diagrams, mindmaps, anything you feel good with and you'll see it clarify.
Of course some tasks are bored and we don't want to do so we loose focus that doesn't mean mental ability.