Just like you, I started programming at the age of 14, also when I got my first computer (although I had been studying for a few months at that point). However, I am "only" 33 now. :-)

My suggestion is that, when developing something, you take each one of those worries (file permissions, number of files in a directory, etc.) and then use all of your vast experience to answer a few questions about it, in this spirit:

• How long would it take to handle that issue properly in your code?
• If you don't handle it properly, how likely it is that this thing will bite you later?
• If it does bite you, what are the consequences?

Armed with those answers, such an experienced guy will not have problems to make a wise decision. ;-)

It is the responsibility of "veterans" like you to come up with this type of requirement, and that involves both identifying what can go wrong and deciding which potential problems you should give attention to.