at 18 is not good but do not worry as there are drugs for reducing the cholesterol.
what is your triglyceride
and LDL level ?
Statins are the drugs to lower the cholesterol but should be taken under physician or cardiologist's guidance.
Diet modification and exercise plays very important role.
Avoid junk food , sugar , oily and spicy food and food containing preservatives like canned food , pickles , sauce , cheese etc
You can have simple curd with brown rice , can put black pepper in it.
Add green chillies , garlic in the food so as to make it palatable.
Fresh juice and soup can be taken.
Eat oats , ragi and whole wheat with lot of green vegetables.
Vigorous brisk walk for half an hour daily and cardio in gym will reduce your cholesterol.
also helps in reducing the cholesterol.
God bless you