We send 18 year olds off to war, so a 17 year old is more than capable of being a highly lethal threat especially when armed with a knife. Try to stab someone and who ever says that they would simply subdue them physically or use a Taser, is taking a huge and unwise gamble with their own life and perhaps that of another. Yes in certain instances up close a highly trained and skilled fighter may be better off closing distance quickly and attempting to control the limb with the knife, but lets face it, that takes a years of practice and even knife fighters or martial artists, will say that you are going to get cut in a knife fight. We all hear about a 21 foot rule and action vs. reaction, but a good way to look at the 21 foot rule is that if you are 21 feet away or less the rule is that you ARE going to get stabbed or cut. Even much further out, if you cannot retreat or place an object between you and the attacker, or mount your own defense and employ it effectively, you still stand a huge chance of serious bodily injury or death.
Relying on a Taser in an up close dynamic situation such as encountering a surprise knife attack at close range is asking to incur serious bodily injury or possible death. Most people cannot draw and fire their pistol reliably in this situation before getting hit and obviously one Officer got cut or hit in the vest from the blade. The pistol is in a position in the holster that is hopefully ingrained in the subconscious mind to perform the draw and it is hard enough to get it out before getting cut or stabbed. Now imagine trying to draw the Taser from a different location that is in an offside position often on the thigh. Taser in this instance is not the correct choice. It is a lethal force encounter and the more correct option outside of physical control, which it sounds like was attempted, is to go to the pistol in an attempt to stop the threat, not the Taser.
There is perhaps more about this 17 year old that the public will not know about as he is a juvenile and will not be made public, such as arrest records, any type of evaluations, etc... and I will just leave it at that.
As mentioned by mf-tom the HPD does not have the old use of force "ladder continuum" which is a bit dated within LE in general, but utilizes a more modern version and the Taser is placed at a higher level of use of force vs OC spray. While the Taser could clearly be an option if you look at use of force as a whole and I will not discount any situation, but clearly in a situation described in the story and it seems pretty clear that the Taser is not the correct option.