A bit of maths that few seem to understand.
Assuming QF remains the same size (and that is anyone's guess), and you don't have more changes to retirement age, the average time spent in each seat (SO, FO, Capt) will be equal to the percentage of the QF pilot population in each rank.
So, from a quick perusal of the list, it looks like there are about 25% SO, 40% FO, and 35% Captains. So, join now, at 25, and retire at 65 (yuk), you'd be looking at 10 years as a SO, then 16 years an FO, and 14 as a Captain.
The fast promotions that have occurred in the past were associated with growth spurts. In the late 80s the fleet dramatically increased in size when the 767 was purchased. More recently some promotions have been associated with basings that were, for whatever reason, unpopular. So, if you want a quick promotion now, I'd suggest mass contracts on the four stripers.