Geohot has a bit of an elitest mindset, despite not really being able to follow through himself. I'd say to anyone starting their interest in the field, don't get put off by this time frame, just keep at it and you will win.
My whole undergrad curriculum was essentially about this, so I would say 3.5 years would be a sufficient amount to study it in depth.
I would say 4.27 years would be a sufficient amount to study intensively.
I'll assume this is only slightly a joke.
People need 4 years of sleep for that kind of dense material to sink in.