Parenting Teenagers (12-18) Support Group
This community is focused on the joys, challenges and concerns faced by parents of teenagers (12 to 18 year olds). The major areas of child development include: physical development, perception and sensory development, communication and language development, cognitive development, emotional development and social development.

If worse comes to worse let him have the atv and take the time to spend so that he is safe..
As far as the ATV, it isn't that he isn't mature enough, it is that it is too expensive for how little he would be able to use it. I would explain that to him. Another option is to give him cash towards one. That way he can work to save the money and buy his own. After he realizes he needs to work at such an expensive gift, he might change his mind.
Unrelated kind of funny story: The 14 yr old got suspended for the rest of the day yesterday at lunch time for having his cell phone out and refusing to hand it over to the assistant principal. I had to leave work and go get him and bring him home. To me, this is not a punishment for someone that absolutely hates school. To make sure he suffered a consequence, I removed the wireless router from our home and took it to work with me so he could not play Xbox live, use his computer or ipod for communication and i temporarily inactivated his cell phone. I got home around 4:30, he's much calmer now and not throwing a fit and he comes to me and asks when he gets his phone and internet back. I tell him the next day (his punishment at home only lasts as long as the punishment at school) he just looked at me and rolled his eyes and said, "I'm bored, there's nothing to do!" In my mind I was laughing and thinking, 'welcome to being grounded' maybe now he'll make a connection with the bad deed and the consequence. I did suggest he do the dishes or vacuum the living room, he just stormed back into his room and slams the door. I didn't think that would appeal to him, but it doesn't hurt to try! :-)
I was always afraid of hurting his feelings or not being sensitive enough to his issues that I walked on egg shells and often wanted to cave into his requests (demands) just to stop the drama.
All our family hunts and we have always had guns. Your older son needs to get into hunters ed if he has no experience with guns and needs to learn gun safety. Yor youngest needs to learn the value of a dollar and be happy to get whatever he gets. You said he has x-box and internet...kid has about all he wants and more.
Sorry for the bluntness but I see your son in how mine used to be. He told me one of his resentments was me not being tougher on him.
Good luck my dear I know you will get this all figured out...)