Re: Zone/Paleo and a young teen (13)
Don't do zone. You'll end up 1) calorie restricting a growing child which is just silly. 2) might give him a complex about blocks and calories, etc, which is just not something he needs to worry about.
Your best bet is to sit him down and explain what are good decisions about the food he eats. It's also a great opportunity to teach him about a goal setting and consequences of his actions (i.e. you eat junk you won't reach your goals).
He should be allowed to eat unlimited amounts of meat, veggies, fruits, tubers, rice and nuts if he has no allergies. Tell him to avoid anything with an ingredient list or that comes in a foil package (i.e. junk food). You admittedly said he doesn't get enough meat, which means he may(or may not) be getting enough complete, useful protein. I'd start upping the meat intake, base more meals around the concept of, half a plate of animals, half a plate of veggies.
At the end of the day though, he's a kid and will probably slip. How much daily exercise does he get? It's too bad you're over in Switzerland as he'd probably be a good fit for american foot ball. :-)