system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek (alternate reality)] Pike: You could be an officer in four years, have your own ship in eight...

Just how exceptional did Pike think Kirk was?  An officer in four doesn't seem that out of hand, but surely the Captain track typically takes a little longer.  There's a little baiting a bravado there, but how much of that process did Pike expect Kirk to shortcut?
gpt
Starfleet (or at least alternate Starfleet) appears to be a bit less rigorous than we'd expect when it comes to climbing the ranking ladder.  If you show you're good enough, if you demonstrate exceptional competence, then you'll be promoted accordingly. The best example of this is Kirk getting officially promoted to Captain of the Enterprise right after the incident with Nero, leapfrogging a whole bunch of more senior and higher-ranking officers in the process.  

So, to answer your question, Pike likely thought Kirk was extremely exceptional. He recognized Kirk's intelligence, tenacity, and natural leadership qualities, and understood that Starfleet's meritocratic system would likely lead to Kirk getting promoted very quickly.