This is supposed to be aimed at high school students.
That's the stated motivation, but like the 40 hours mentioned around the same place, I have always assumed it was intended to be a bit tongue-in-cheek. The material covered here would span much of an undergraduate syllabus, and it would surely take several years even for an interested and hard-working mathematics student at a top university to understand and apply all of this effectively. Indeed, there are references to concepts that you wouldn't necessarily expect to have studied in detail or perhaps even encountered at all below postgraduate level.
That's the stated motivation, but like the 40 hours mentioned around the same place, I have always assumed it was intended to be a bit tongue-in-cheek. The material covered here would span much of an undergraduate syllabus, and it would surely take several years even for an interested and hard-working mathematics student at a top university to understand and apply all of this effectively. Indeed, there are references to concepts that you wouldn't necessarily expect to have studied in detail or perhaps even encountered at all below postgraduate level.