I'd suggest a newer game, if memory serves you still need to put +mlook into the console for Quake and the less effing about the better when you're learning - but if your son has it already and can turn mouselook on, go for it.
The way I learned, the friend who taught me said that if I got the hang of circle strafing, everything else would be a breeze. Circle strafing is when you basically rotate around a target shooting at it (like an angry moon around a sun) - you can use any stationary object in the game to practice - basically, you're just moving sideways with A or D and using the mouse to keep looking at the target. Don't worry about the shooting bit until you have the motion down pat.
If you can nail circle strafing outside the distraction of combat, you will find everything else falling into place and you'll spend a lot less time looking at ceilings and floors. If it's too hard, turn the mouse sensitivity up or down a bit until it feels better. Chances are, over time you'll want to increase the sensitivity so that a sharp sideways motion brings you about in a 180, but that's probably too fast to start with.
-- boobs do nothing for me, I want moustaches and chest hair.