Remember that in Sweden, the driving age is 18, which makes Swedish PCs less mobile. Couple that with very limited access to guns, and you have teenage characters that wouldn't be too powerful. I remember some stupid sh*t my friends and I did in our upper teens, so don't discount those years. The problem here is the question of scaling the threat level; a 12-year old kid is way less capable than a 17-year old. If you run a campaign, with a mystery or two each year, stretching it out over 5-6 years, a GM could up the challenge as the Loop is causing more and more trouble.
None of this surprises me but the access to firearms. Really? I'd have guessed there would be a hunting culture in Sweden, since it's even a point of tourism. Growing up in Canada, I was faced with the same deal, finding a weapon for me at 12 was incredibly simple. Though Combat is definitely not the point of this game, as it's stated itself. I would place a lot more stock in there being traps and gadgets, as well as distractions. Like firecrackers or bottle rockets before you get on your bike and bolt.
As for driving, in Sweden there's AM Driver permits you can get at 15, and A1 you can get at 16. So tractor trucks and mopeds, at least on the older non-adult PCs. Even then, breaking the law can be a great part of an adventure.
Wouldn't have it any other way, but damn is it cold today.