A speech/language pathologist may be able to help. My understanding is that sometimes young men are so surprised by the change in their voice at puberty that they suppress it. Don’t know if that’s the case here.
I have a moderately deep voice but I have noticed when I answer the phone at a friend of mines shop my voice goes up about 3 octaves. She has a much snooitier clientele than what I am used to and it affects my voice trying to sound nicer. Voice coaching could probably help him with this.
Voice coaching is definitely good if there’s no biological problem. But I would definitely suggest getting that checked out, too, if only to make sure there’s nothing wrong. Though, hopefully, a good speech pathologist would do that anyways to rule problems out. They wouldn’t want him to damage his voice.
Luckily, it’s easier to go down than up, oddly. It’s easier for a higher pitched voice to sound more masculine than a lower pitched voice to sound more feminine–to the chagrin of many trans women. (And trans men get hormonal therapy that deepens their voice.)
Is it a personal peeve, or is his voice really unusually high? if it is, and he also is short on secondary sex characteristics, he might need hormone treatment. There is another very rare possibility, but I know of it because I have worked with the disabled population. I have known two men who spoke in falsetto after a head injury. They couldn’t not do it, and didn’t really hear it themselves.
If his voice is really unusual, or unnatural, he might want to see a doctor.
If it’s just that he happens to be a tenor, and not a bass, I’d go with voice coaching.
Cigarettes and whisky can backfire by causing nodes that give you a gravelly voice without lowering the pitch much. In other words, he could end up sounding like Lucille Ball or Suzanne Pleshette toward the ends of their lives. Not to mention cirrhosis and lung cancer.
Everyone has a range. A voice coach can stretch your range a little, and help you to use your lower register more and avoid your higher register; after practice, it becomes natural. I knew a woman who saw a voice coach to prepare for a college production of Victor/Victoria. She had a great “masculine” sound for the “Victor” parts.