I don't know if it really matters if you are 20, 40, or 80; we can get caught up in certain traps no matter what our age is. Experience is definitely something we should be able to tap into later in life, but we can be stressed and feeling like we need to do much more than we are capable of even when we are 'old'.
I have a little startup and I keep a 'TODO' list of features to implement, bugs to fix, things to test, documentation to write, etc.. I could stress out because the list never seems to get any shorter. Every time I cross one thing off the list, I think of two more to add. Instead, I try to focus on what I can accomplish that day (or that week) and stop when I have spent a certain amount of time on it.
If I am in an ambitious mood, I might speed many hours tackling a single issue. Other times, I can go a whole week without ever opening up the IDE. That is OK! I have the luxury of not depending on the startup for financial survival. I also realize some others do not share this freedom so I don't criticize them if they feel stress and overwork on their project. I just work at my own pace and try to gain satisfaction on what I am able to accomplish.
I try to apply this technique to other areas of my life as well.