I have an 11 year old son who has had nose bleeds on and off since he was about 4. Like your son, there was a point a couple of years ago that they were very frequent, probably more than 12 in one month! He does have seasonal allergies and takes claritin semi-regularly. He sometimes wakes up in the middle of the night with them too. Other than that he is a normal, healthy 11 year old. I also had frequent nosebleeds as a child. I was probably in my early 20's when I stopped getting them. Maybe it's some sort of hereditary condition?? although I have a nine year old who has never had one!