I think these theorys are much more complicated then need be. Here is mine.
The academy period is five years that's basic for everyone. on this time period the teachers teach the students the basic requirements for being a shinobi. Then of course especially at later years of the academy each student trains by himself when not in school. For example Sasuke learned his fire release, Shino to control his bugs, Kiba his combo attacks with Akamaru and Naruto learned... to do a harem...
How come Itachi graduated at 7 then? Well itachi was one of the most talented seven year olds Konoha has ever seen. He was an incredibly quick study and trained a lot on his own. This made him easily surpass the knowledge required to graduate LONG before kids his own age who most likely took 5 years like everyone else. That's why an exception was made for him. It's most likely not the first time this has happend and most likely not the last. But it isn't something that is usually done.
So Sasuke is disapointed that he is "just" the top of his class with perfect grades. But still isn't good enough to graduate early. This also explains why it seems as if all rookie nine graduated simultaneously. They did.
Also do note that Team Gai is one year older then the other k12, they graduated a year before the others.
