Upgrade is tough to determine. If you look at it as a pure numbers game you can only get an estimate.

My seniority coming up on 9 years and well over 550 away. ( not from the most senior non GV captain). With no growth plan and attrition at say 2%... That's roughly 10 more years minimum..for a total of 19 years. Sure there may be several dozen bypasses which may allow someone to sneak in ahead of their time. What if attrition is 1%'or less? Do the math.

A new hire will may see a bit shorter times because of the 4 yr gap in hiring