Whilst there are people who will get FO slots almost immediately, they will then spend a long time in that seat.
Assuming the airline neither expands nor contracts, then the average time in each seat will be related to the proportion of pilots in each rank. So, as it is probably roughly 33% each, then the average career would be one third in each seat. So, I'd suggest that the 12 year SO is very much the average...and the 7 year wide body Captains are very much ancient history/mythology at this point.
The uneven recruitment has built lots of bumps into that though, and the people who joined in the expansion of around 1985 are hitting retirement age.