Why is it mainly older men in rural areas? ACCESS TO HEALTHCARE.
Rural people tend not to have benefits, they are generally not working in the city for big companies and there is less of a chance that they have benefits. The support by the current medical system for mental health is almost non-existent, if you need to talk to someone about your problems it cost you a ton of money, another thing that rural people tend not to have a lot of kicking around.
The reason why they use guns is because guns are what they have. If there were no guns they would jump off something or cut themselves, men unlike women, tend not to use pills but women rarely do something that will leave an ugly corpse, not sure why but this is the case.