#1 It doesn't matter how old the offender is if you decide to defend yourself. Whether he was 16 or 18, you can use REASONABLE force to defend yourself and your property.
#2 Pepper spray is a good self defense weapon, but it could potentially be lethal if the offender is asthmatic or has some other type of respiratory problems. Also, pepper spray is non discriminatory. If the wind is blowing in your face, you will get a blast of it too. If you hit the inside of your door, it will be inside your camper.