What on Earth? Masturbation is always a mortal sin! The only exception, and I'm not even sure about this, is if perhaps the kid doesn't know, he was improperly taught, but it's hard for me to imagine that happening in trad circles.
Just because there is more pressure on young men today and perhaps more temptation doesn't make masturbation less of a sin.
Luckily for them penance is less harsh than it used to be, so they can confess and try again until God perfects them and they overcome their offensive habit.
I grew up thinking that boys "had" to do this, and was surprised how easy it was to overcome it with grace. It is a huge falsehood that self-abuse is somehow an irresistible impulse. This is to encourage people in their weakness, instead of to teach them to trust in God's grace. Of course, I know you're not saying that.