You said your son doesn't want to talk about the facial hair problem. I'm wondering if he is embarrassed or frustrated about the hair, or if the hair really is not an issue for him. I'm guessing he might be embarrassed or frustrated. Yes, guys want some facial hair to make them feel "more manly" or grown up, but too much hair can cause teasing by peers. He might not be sharing this if it has happened at school. Kids can be mean and call other kids names like "gorilla man" or "monkey boy". If his self esteem and personal confidence are strong he'll deal with it on the outside but it might gnaw on the inside (emotionally)and likely not be something you want to tell your Mom. Your relationship with him is important so you can get to the truth (his real feelings) without more embarrassment or frustration. Be sure YOU are the right person to talk to him, or perhaps his Dad or trusted Uncle- someone he looks up to and willing to share his feelings with, would be a better choice. Give that some sincere thought.
If he is embarrassed or frustrated then finding a solution is imortant. Talking to a GOOD barber that will provide a pleasant experience and wise advice on "how to" and where to get quality equipment is a step in the right direction. You can talk to a dermatologist about hair removal that will permanently remove or reduce the amount of growth. Women commonly deal with hair removal in that way- works for men too. They might also recommend a cream that leaves the face smoother- longer. If he wants the hair removed, there are ways to do it that don't involve the everyday boredom and frustration that teens and early 20's don't want to bother with.
If he likes the hair on his face, then finding a "hip" style could provide the motivation to trim it up.
There are lots of directions to go with the facial hair issue but I think the first avenue to follow is an open, honest conversation about how he really feels about the hair growth, and what he'd really want if it were up to him. And please, don't make this a point of casual conversation around family and friends until you know what he's really thinking. This really is a kind of personal issue
Good Luck. hope you find the right solution. Look forward to hearing how this turn out.