As far as youngsters defending themselves with home firearms, I would say I'm for it with some caveats.
When I was a kid that age, and we (my little brother and I) were left alone, Dad always said, "You know where the guns are if you need them," before he would leave. Then one night I remember one of those news magazine type shows coming on TV. It was Dateline, or 20/20, or 60 minutes, or something along those lines.
One of the stories featured some youngsters who were home alone (in their teens, capable of being left alone for a while), who had what appeared to them to be a crazed person trying to break in. I can't remember the details now, this was better than 15 years ago, but IIRC, I believe one of the youths shot the man. Afterwards it was found out that the kids' parents had been in an accident, and had asked this guy who was at the scene to go to their house and inform the kids, because the parents were being taken to the hospital. Again, I was a kid when this came on TV, so I may be fuzzy or incorrect on the story, but it was something along those lines. I'd love to find a link to a transcript or old news story about it, but I can't remember enough details that would make for a fruitful internet search.
What I do remember clearly is that after that program was over, my mom and dad needed to go run a few errands, and normally they would've left us at home, but they wouldn't let us that time. They made us go with them. Dad wouldn't give a reason when I asked "why?" but I knew the answer.
I see no problem with a teen defending himself/herself, but a teen's maturity level and ability to correctly size up a complex and dynamic situation is not always as good as an adult's, and even adults' can be lacking.
I don't know. I'm with Pax on this one. Not sure if there is an across the board "right answer." I suppose it depends on the maturity level of the kid, and the complexity of the situation.
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed." -Amendment II, Constitution of the United States of America