For those who might be interested in the decline in VO2Max after 50 years of age, this is my experience having just turned 60. The 2000 m indoor row is a good proxy for determining VO2max as world class athletes go under 6 minutes (not me ) which is considered a typical VO2max effort.
Every year I start a rowing program in mid-September and target the CIRC on the first Sunday in February (Canada). My training programs have varied but I always feel like I couldn’t have done much more work to prepare for the race and then during the race it was a RPE of 10/10. I trained 5 to 6 days a week on the erg during this period building towards a peak for the race. It is the only erg race I do every year and afterwards I switch to road bike training. Most variables such as weight, health, etc. I would consider stable though the history shown. Years without results, I couldn’t race for some reason.
A researcher developed a correlation between VO2Max and the 2000 m indoor row performance and I have used the calculator linked above, to determine my numbers (which agrees to other testing I have done through running). You can see from my results that my performance decline has been a about 1.2% per year from age 50 to 59. I started using training plans around age 48 and as a result, my times improved from previously unsophisticated training years