It all depends, mostly on two variables: forward growth and age 67. Assuming the retirement age stays at 65, and the current trend of about 80% system seniority for the first opportunity to upgrade to Captain holds (Look here for data on the last 31 bids with a graph and trendlines), it will take somewhere around 8 years for a NH today to reach 80% with no growth, or around 5 years with 2% growth (a more likely scenario). "Ish". If the retirement age goes up, those times will extend by roughly the same amount as the extension (maybe a little less as not every 65 year-old will continue to 67.)

80% is a good, proven planning factor. There have been times when actual awards have gone both junior and senior to that 80%, so YMMV. Also, future wide body deliveries may shift more NB captains to WB, which will open up seats for things to go a little junior over time. (Remember the 787 doesn't even begin to show up until 2031 at the earliest. Some 339 and 359's will show up in the late 2020's.)

FWIW, by historical standards, 5-8 years still pretty fast. Post-Covid upgrade timing was crazy, but is a historical outlier due to incredibly fast hiring - 5000 pilots in 2 years will do that. Also, the crazy fast MD-88 awards just before Covid were also fast for a reason. But on the flip side, the 'lost decade' (9/11, Bankruptcies, and 60>65) saw incredibly long times at 12-15 years. The lesson there is, it's always changing...