Anecdotal, but as a somewhat senior (yet still relatively new to Delta) NB FO that bid better and better REG lines, I found myself flying with more and more senior captains. While it wasn't all bad, it was interesting how the dynamic shifted towards "I'd like to fly with that person less" as I bid more senior-type trips.

Then I switched to bidding reserve, and if I fly at all, it generally trends towards more junior trips. It has been like a breath of fresh air, both in schedule, and who I end up flying with. I'm not age-biased, and was hired later in life than most.

Wait, what was this thread about again?