As an old-home owner and a hobbyist woodworker, I can confirm that it’s not user error — old-growth timber really is that dense. Even my impact driver struggles to drill simple holes sometimes.

I have very good drill bits. Old growth wood is like nothing you've ever seen before. I'd rather have a house made of it than anything else. Stuff is as hard as a rock. Harder I'd bet. My drill has no issue driving through metal. The thing about old growth wood is that as you drill in, the hole gets 'smaller' behind you. The wood fibers are highly packed together. When you make a hole, they sort of expand behind the bit. If you're using a spade bit, it can even be hard to pull it back through.

I'm also an amateur woodworker, and if you've ever dealt with ipe wood from Brazil, old growth pine is harder than that. I made a nice mantelpiece out of ipe and my bits had no problem with that. Old growth pine is very dense.

Around here people use hedge wood (Osage orange) for fence posts. It's hard/dense to begin with, and after weathering for 20 years outside, it'll make your chainsaw chain spark if you try to cut it.

It even gives carbide chain a run for its money.