Hi wahwah,
Usually risk factors for cholesterol is divided into what's called modifiable and non-modifiable risk factors. Non-modiafiable is things that you can't do anything about, such as age, sex, family history, personality type. If family history is the problem, there is a problem with the way cholesterol is 'made' in the liver, that's why medication is usually the only option. Modifiable is the ones you can do something about, such as excercise, weight, diet, smoking, diabetes (sometimes), etc.
Usually GP's will ask a patient to try and modify their lifestyle first to see if it makes a difference to their cholesterol levels, unless it's very high, where it meds right from the off. The meds have their side effects too... I'm sure if you google a bit you'll find loads on this.
It also depends on the 'make-up' of your total cholesterol level. It's made up of loads of different types of cholesterol, good and bad ones. We actually need them, every cell wall is made of fats, need them to make hormones, etc, so not all fats are bad. What you want is high levels of something called High density lipo protein (HDL) and low levels of Low and very low densty lipoprotein (LDL and VLDL), there are a few other too but these are themost important ones to worry about.
So, getting to your son... good habits to get into... excercise increases HDL and decreases LDL's (usually),
NO SMOKING, ever, increases LDL (in liver)
Diabetes is bad news, apart from the assosciated health problems it changes the way the body metabolises fat so increases LDL/VLDL, try and do everything to avoid getting type II diabetes.
Diet is very important. Basically, avoid animals fats like the plaque (except fish, plant fats is ok. Meat should be lean (think chicken without skin, pork where the fat is usually a rind that you can cut off). Want you want to do is increase his intake of something called mono- and poly unsaturated fats, usually found in plants, and keep his intake of saturated fats to a minimum. Also, fibre is very important. Two types again, soluble and insoluble. Insoluble does exactly what it says, in one end, out the other, something like shredded wheat, weetabix, etc. Important for bowel health amongst other things. Soluble fibre on the other had is the stuff that does the job for cholesterol. It's a jelly-like substance, the stuff that makes porridge congeal when you cook it, and gets absorbed by the gut and 'mops' up cholesterol. A good intake of both is very important, esp for men to prevent things like prostate and bowel cancer. Good sources of both is things like veg (some have both), beans, pulses and, drumroll, the best thing ever...oats. Good old porridge is your best friend! Baked beans on brown bread is almost a perfect meal, great protein, carbs, right fibres. And then there's the stuff in things like Benecol and Flora, called plant sterols, that modify chlesterol in other ways.
Loads available about all of this on the net, and information is your best form of attack! This would be my advice for an adult though, and it's a long time since I worked with any of this, so please check it all out for yourself. Perhaps you should ask your GP for advice considering your son is still so young, referral to a dietician perhaps? Best of luck, you will give him a great gift if you can foster these habits in him from a young age.
HTH