Is my old beer mix still good for brewing?

I just brewed a Chinook IPA kit (LME) from Northern Brewer that's been on my shelf for over 6 months. Granted, it's not an AG batch but the consensus is that "old ingredients" do not produce optimum results and I can attest to that since this batch did not turn out well. It tastes like a mix between a pale ale and a stout. SRM is way darker than usual too. Nothing like the previous Chinook kits I've brewed.

You could always try your kit and see what happens but most likely the ingredients are just too old. Think of the difference fresh basil (if you've ever had it) makes in a pasta dish compared to something from the store that's been dried and sitting on a shelf. And then been in your cupboard since 2013.. ;)

I'd consider throwing them out entirely. Grain will stale over time. Typically it should be used within a year or two, otherwise it will take on strange flavors from staling. If you're curious, you can munch on a few kernels to see what it tastes like. If you don't mind the taste, you could still brew with it. But my bet is it will taste "off".

If you have any hops in the kits, they are all rubbish, same as the yeast.

You're always better off using all fresh ingredients. You might be able to create a marginally acceptable beer from old stuff, but it's also kind of a waste of the time it took to brew if you aren't producing a beer that is at least fairly good, and potentially great. When you use fresh ingredients, the odds of a good beer are obviously much higher.

Choice is yours on the malts, but I'd probably not use them. Throw away anything else in the kits.