Guns are certainly not my area of expertise. But this paper -- which may or may not be reliable, and admittedly is well out of date -- suggests that about 30% of handguns are stored loaded and unsecured, and 37% of handguns are kept in bedrooms.
"Guns in America: National Survey on
Private Ownership and Use of Firearms
by Philip J. Cook and Jens Ludwig"
Editing to add: People who are willing to physically hit someone with their fists or a held object are usually not the type to feel 'trapped by a friend'. Guns, on the other hand, are a distance weapon requiring no physical contact with the other person, so psychologically may be more appropriate for such a person to use as a threat.
I guarantee the real number is far, far above 37%, but not in a teen's bedroom. An unloaded gun is just a poor club, and a secured weapon is useless, even for a club. There certainly are some, but I am an expert, and I don't know a single gun owner who doesn't keep a loaded, unsecured handgun in the bedroom.
The number of people buying firearms of all sorts has gone up
dramatically in the last six years from fear that a democratic controlled government would place more restrictions on certain types, including handgun.
Teens can legally own a gun, but can't actually buy one until he's eighteen. I started hunting at age seven, and owned my own rifle and shotgun at age eight. I also had full access to a revolver at age ten. This really isn't uncommon, but it is uncommon to have a handgun stored in a teen's bedroom. Technically, it isn't illegal in the majority of states, but it can be used against the parents, should something bad happen, be it accidental or intentional.
The psychological part is difficult. I can't remember a single case of one teenager shooting another in his own home out of fear. We've had a number of accidental shootings, but that's about it.
In most states, you can legally shoot someone for three reasons. 1. If you legitimately feel your life is threatened. 2. If you have reasonable belief that you will suffer severe physical injury. 3. In defense of property.
If this is a gun owning family, it is possible, even likely, that a teen would have a rifle and shotgun in his own bedroom. It's somewhat unlike, but possible, that he would have a handgun.