You'd hope it was true. Big O is a high-profile saint, with the best advice available to him, and certainly no fool. And yet, he appears to be wrong. He appears to be so badly wrong that I suspect I've made some obvious mistake; if so, please point it out to me1.
Here's a picture (the one below, not the one to the right...) from the CDC site. As expected, the wrinklies die of disease, but for the moment we don't care about them, we care about the young folk.
As sort-of expected, homicide peaks for late-teens / early adult, presumably amongst young men who make regrettable life choices. If I split by sex, we'd probably se something different for the rather more sensible female types <tries it> Ah yes, the sensible women are more likely to kill themselves: H+S = 27% for 15-24, vs 44% for males.
I don't think switching attention to the 10-14 group would help the argument. I wonder if you adjusted the breakdown, you could get something that looked like Gunz-are-Number-One: for 1-14, UI leads, but contains 27 "firearms"; Suicide (#2) has 189 F; Motor Vehicles leads UI as 294... ah, but if you broke MV down into all its constituents, the leading number would be 87, which is less than F. I think that's cheating, though.
You'll be wondering, of course, if "Unintentional Injury" hides some Gunz Deathz.
But no. UI is mostly Carz, with somewhat oddly "Poisoning" coming a very close second. But that's because P includes Drugz. For 10-14, F-in-UI comes up, but only to 5%.
0. The gravestone is from SEH.
1. There was no shortage of kind volunteers. See the comments. And see my update.