Screen Door Challenge

I've come to the conclusion that I've not the same person that I was 10 years ago, which in some ways is a good thing. But there are things that I've noticed that are not so good. Now we had another busy weekend and on Sunday I set myself the task of creating a screen door for the back door of the out house. Something that I thought would be easy as I've always considered myself reasonably capable with my hands. Maybe its the fact that I've never done this before, or that I can't remember the last time I did anything with wood. Maybe its the fact that I had to stop and start the job though out the day so I never really 'got' into it, but its taken ages. I think I could have built the side of a house in the time it has taken (even with my slow bricklaying). But hey presto after a few silly mistakes, like making it 1 inch too large at the top. The door was complete, and most of the day was gone. All the other jobs that I needed to do will have to be put off now, which I really wanted to get out of the way.
So is my memory shot and I'm confused about what skill I did have? I am I becoming decrepited and I don't have the same capabilities I did have 10 years ago? I am I really making to much of this and I should put it down to just having a bad day. I don't know, and now that I've written this out I'm not sure I really care that much. Its done and built, I've voiced my views and I can go back to my day feeling some what vented. Oh attached is a pic of the lovely door... ain't it grand.... (I've also corrected my bad spell now).