Uh huh... I don't actually get what your point is? If you look at figures that aren't 7 years old, you'll see that guns have overtaken motor vehicles as the leading cause of death for under 18. All the justification around that doesn't change it either.
Guns don't kill people. Criminals kills people (after all, accidents are shown to be minimal, even suicides aren't that big a factor, and it's not like homicides disappear in countries with gun control, see Mexico). That's the point. While the clickbaity term "leading cause" really means "something like 15-20% of total because other causes are classified in a fragmented way".
Long story short, no matter how you justify, you are trying to use journalism 101 manipulative tricks, that is a fact, and even CNN tries to be more subtle with it now.
How do you think the numbers compare with other countries?
What other countries have US style gang culture in its cities and on similar scale? Honduras, Brazil and the like? Those might be worse.
Also, if you want to talk about gang related stuff, two of the common arguments against gun control are that "Then only the bad guys will have guns!" or that "If they get rid of guns, they'll just use knives or whatever instead! Should we get rid of those?" so presumably we should see similar youth death rates to firearms, or knives perhaps, in other comparable countries right?
Don't think many places that do have a similar social problem, like Honduras, even bother with such detailed statistics.
Still, it's a step in honesty, and also, compared to the above, due to said honesty a far less acceptable political pitch.
Imagine if democrats were selling gun control with "Teenage gang members in the cities run by our crappy politicians and raised by crappy parents who vote for them and crappy schools run by unions that love us, are killing each other a bit too effectively, and so we have to restrict the rights of all of you, so that some 25-50% more of them can live to do gang stuff another day. No, we won't be doing stop and search and locking them up, that would be racist, wtf".