Update: The estimated VO2max value continues to go up, gradually. The new number is 59.1, versus last week's 58.6. I also set some PRs this week (and some "old guy 65-69" KOMs), which lends some validity to the upward VO2max trend.
About that "old guy leaderboard": Some of the guys on there were much faster than me 20 years ago, so maybe I'm now training more than they are. Or maybe they're not trying as hard. Either way, I'm taking the "W".