Yes, it's fine for him to eat Paleo. There's no reason for him not to.

If he's highly active, you may need to increase his carbs (boys, especially, lose weight really easily on Paleo, it seems), but you can do that by keeping fruit, potatoes, and other Paleo carb sources around for him. Make your own fries from potatoes and sweet potatoes, make mashed sweet potatoes, etc. If it's tolerated and if you want, you can even keep white rice around (often considered a "neutral" grain, because it doesn't really have the anti-nutrients that brown rice and other grains have).

As for "easy to make" stuff, you can do a lot of the same things you probably do already, just nix the bread and eat it from a bowl, or lettuce (or bacon) wrap it.

I 100 % agree with dragonwolf on the higher carb for growing boys and man in general. My son almost 5 and he is already on the low end of normal weight and my husband is a skinny fat , who used to be severely underweight and even the worst SAd diet he never been obese, so they need higher carb.
I cut out wheat and bad grains, but I kept the white rice, and all kinds potatos for them, and they eat a lots of fruit.

I also bake paleo goods. I bake coconut paleo bread /tortillas and almond flour muffins and even some cookies for them.
I know many paleo people despise paleo baked goods, but it makes the transition so much easier for kids and family members who are not 100% on board and can not leave the idea of sandwich behind (yet?).
I think paleo coconut bread/tortillas are a good compromise , as they only have coconut flour, eggs, salt, baking soda , but no sugar if you end up eating it is fine. Paleo tortillas great for making pizza and even quesadilla if you keep the cheese for them, which I do. Coconut flour is like a sponge it takes so many eggs, and very easy and fast to bake. A half cup coconut flour absorbs a dozen eggs and makes a dozen 4" flatbread. I make it on the weekend when the oven already on for a roast , and gets my me through the week making sandwich for them.

Of course the muffins and/or cookies have honey and/or maple syrup so they high in (natural) sugar, so that is a bit iffy if you can not resist them. I no longer crave them, hence I do not mind keeping those around. I bake sweet stuff from almond flour once a month in a large quantities and freeze them in small batches, and just pull them out as needed. Freezing actually improves the texture and they defrost super fast.

I have a two year old and a husband who is 6'3 with a very healthy appetite, and since I am the main reason for switching our household to a healthier way of eating, I've definitely dealt with the same kind of issues as many parents here have, I'm sure. What i discovered, though, was that my son loves cherry tomatoes, sugar snap peas, carrot straws, meat and cheese rollups with mustard for dipping... we do have the occasional PB&J when we're out and that's the least-worst option, and even with my own eating I am not 100% strict paleo. But mashed sweet potatoes with butter and bacon crumbles on top? He's sold. So just try to add in new things as you go, be flexible, give him the chance to try and taste and have his own opinions. My son doesn't always eat a ton of food but I do notice that when we're out and about, he's all over the fig newtons/oreos/breads/crackers because we don't get them at home.

Give it time. You will come up with good ideas for him and especially so if you involve him in the decision-making process. 12 is a great age to learn some good cooking skills and if you work together to pre-prep things you will have much better success. For example, you two can chop and steam-sautee veggies like carrot circles, chopped red cabbage, and spinach, then top with cooked ground beef and some cumin, cheese if you tolerate it, and your own mix of taco seasonings for an amazing meal that you can portion out and freeze. If he can operate a microwave he can heat a snack like that for himself. I just think Meat + 2 Veg + seasonings = yum. Lol. But I am lazy.

Yup, dump the non-food. Health is priceless.

My child eats Primal/Paleo. Children will of course resist change- remember: you are the mom- but this lifestyle is absolutely healthy for children. Since I enjoy a ketogenic version of Paleo, I do allow my child more things than I allow myself. She eats more fruit and I even let her have rice, potatoes, and organic popcorn (this is where I cave in too) a couple of times per month. I also make homemade granola bars that do have natural sweetening in them, but I reduce by half what the recipe calls for.

There have been vast improvements in my child's behaviour and health since making the change 16 months ago.

Here is a free (today) kindle cookbook called Paleo for Kids

http://www.amazon.com/Paleo-Recipes-Kids-Afforadable-ebook/dp/B00FP7P67A/ref=sr_1_5?s=digital-text&ie=UTF8&qid=1382013267&sr=1-5&keywords=paleo

I'm gradually transitioning my kids. As of now I have them gluten free other than my daughters bread addiction. My husband won't let me stop buying it. We have made a lot of progress still despite the bread. In the next few months I hope for a paleo home. My husband is the only barrier and his only vice is he feels he has to have it bread. We will make it all the way eventually. It's so hard to change their diets. It's best though. No doubt.

I'm gradually transitioning my kids. As of now I have them gluten free other than my daughters bread addiction. My husband won't let me stop buying it. We have made a lot of progress still despite the bread. In the next few months I hope for a paleo home. My husband is the only barrier and his only vice is he feels he has to have it bread. We will make it all the way eventually. It's so hard to change their diets. It's best though. No doubt.

It might help to switch to a gluten free bread, such as Udi's in the meantime. At least that would get them off the gluten stuff entirely.