My non-confident guess is that most mathematically talented people encounter algebra and other subjects long after they're ready for them, and therefore learn them fairly rapidly but at the cost of having wasted time earlier on.

That might explain my experience in tutoring my cousin in math. I find he is able to catch up quickly once I explain the background material a given concept is based on. So, if he had been ready for some time to learn the background material, then learning it when I present it is not a big deal and doesn't even noticeably detract from the effort and focus he needs to understand the new concept he is supposed to be learning.