Hi Annie. It's called bumfluff to those of us who had to go through that phase.
The wispy haitrs on your son's top lip will get thicker and thicker until he comes home from school one day and tells you (with much indignation) that he's been told to shave! He'll be about 14 or 15 then. Then you can buy him a razor.
Please beware for his sake though. Your son will think it's a great laugh the first tiime he shaves - and it will be for the first hour. Then the pain starts! His whole face will become more and more sore until he can't stand anything to touch it. That's due to the shaving taking off the top layer of skin cells! It sounds awful but it doesn't take too long for the skin of the face to become accustomed to the daily assault. Adult men don't think twice about shaving but I still remember the pain.
I'm sure you know that your son will try several different shaving methods such as disposable razor, electric shaver, rotary head, foil etc. He''ll soon settle on which method he prefers and he'll probably stick with that for the rest of his life..