RS,
I haven't made the effort to keep up with most airlines and their upgrade times. I hear some pretty wild stuff coming from Delta with people upgrading within a year or two. My son who's in his 4th year could hold captain on B717 and A320 in KATL and B767 capt in KLAX (IIRC). Some people have gotten an upgrade with far less time than that.
I would issue a caveat to these stories and will risk telling you something you already know: These events are FAR from the norm here. Do not be misled or even encouraged by them as they can radically change before lunch time today. The first time the economy takes a dump and positions get cancelled, these VERY junior, out-of-seniority upgrades will find themselves back in the RHS in a flash. Or if lots of people who could hold captain but have passed it up for one reason or another decide now is the time, these Wunderkinds will get their captain position cancelled and get bumped back to a position more in line with their seniority.
So, it's fun to watch while it lasts but the question is how long will it last. No one knows...don't plan on getting in on it.