1. baking powder was so far away from fresh
2. recipe said marble-sized butter chunks, so that's what we did
3. I think this is the problem
4. yeah, it was folded
5. all-purpose- almost bought cake flour for the decreased protein but the recipe said either or
6. this was also the problem So I think it comes down to butter. I had it super-cold (not frozen), but I was working next to the oven which is really poorly insulated and sheds heat like a mother. Also no A/C in the house, because this house is a 70 year old disaster. So we worked as fast as we could, but that dough gets warm even faster. Also, I think I rolled it too thin- recipe said half an inch, it was less. Put it together, you have a thin dough that heats through at the drop of a hat next to an oven that doubles as our main heating element in the winter. DOOMED.
In addition to humanodon's fine advice, I will also add: 1) The more you work any kind of dough, the tougher it will get. You want to go with the absolute minimum. 2) Butter should be cold-cold. Super-cold isn't that important. Working quickly is. You should go from ingredients to rolling in about 4-5 minutes tops. 3) I know Alton Brown hates the shit out of "uni-taskers" (but have you ever seen his measuring cups? WTF) but a pastry cutter is impossibly handy if you're going to make pastry. We've got a wire one very like this. I guess Oxo has a fancier one for ten bucks. Never used it. "Marble sized chunks" is bullshit. you want aquarium gravel or smaller, and you can't get that without a pastry cutter.
Those biscuits may be doomed, but notes can be taken for next time. Next time, once the butter is cut in to the flour, throw it in the freezer for half an hour. Then pull it out and add your buttermilk or milk, mix it real gently, turn it out, but work it as little as possible. I like to just pat it out, carefully fold it over itself and then gently pat it out again before cutting the biscuits. Working with butter can definitely be a pain in the ass.