Stick length is based so much on preference. I'm the same height, and my sticks are about mouth height when on skates. I know others about same height who have it to their throat all the way up to their nose. So it can be all over the place. Throw in factors, such as lie, flex, playing style, position; it gets even more varied.
For your son, I would worry more about flex first, and go from there. At 125lbs, unless he's really strong, he's gonna need a pretty low flex stick. I concur with some of the other posters who said to check out intermediate sticks. You could also check out pro stocks as well. I've seen senior pro stock sticks all the way down to 60-65 flex. Retail senior sticks, the lowest you'll find is 70-77 flex, and at 5'-9", you'll probably end up cutting a few inches which will bump up the flex rating 3-7 flex (depending on brand). Again, unless he's really strong, retail senior sticks will be too stiff.