OSDev.org

I think a 5 year old could do basic code no problem assuming they had decent reading/writing ability's, let's just look at DOSes batch...
Not to hard, a basic understanding of that would not be hard to comprehend, I mean theres like no syntax there either... Now doing something like actually making something such as 99 bottles of beer on the wall would be more complicated, because you'd need to do a loop that could keep track of the bottles and knew when to exit, not a very hard concept for the experienced, much more thought for a child, however maybe if they played around enough age 6 or 7 99 bottles of beer on the wall may not be very hard...