VO2max is mostly a vanity metric
Mine went 44.2 to 61.3 in a year according to my watch and I absolutely checked it every week, so I'm not above this. It has since dropped to 55 in the summer heat while I'm the fittest I've been. Yes VO2max is a real ceiling, no it's not stopping you from getting faster.
It's real and it matters, it's just not the thing to chase. It's the size of your engine, not how much of it you can use or how efficiently, and unless you're already elite something else gives out long before you get near that ceiling. Also your watch is estimating it, not measuring it.
What it actually is
The most oxygen you can take in and use per minute, which really is a ceiling on how much fuel you can burn aerobically. The problem is that a ceiling only matters if you're up against it and for basically all humans you're going to hit some other limiter first in real world performance.
The big three, of which this is one
The standard model here is Joyner and Coyle's, and it's held up for decades: endurance performance comes out of three things, not one.
Economy is the one nobody posts about and the spread is enormous - the oxygen cost of running at a given speed varies 30 to 40% between people. Two runners with identical VO2max, one 30% cheaper per mile, and that's the race. There's a longitudinal study of elite distance runners where VO2max was unchanged after one, two and three years while race performance improved anyway, because economy and threshold kept moving underneath a ceiling that sat still.
Two things people bring up
Genetics. HERITAGE put 481 sedentary adults through twenty weeks of identical training: mean gain about 400 ml/min, but some gained nothing and some over a liter, roughly 47% heritable. Low responders are real. But that measured sedentary people over twenty weeks - if you've trained two years and plateaued, you're not a low responder, your ceiling just arrived before your threshold and economy did.
Longevity. The Cleveland Clinic cohort of 122,007 people found the fittest group had around 80% lower all-cause mortality with no upper limit, which is enormous and I'm not arguing with it. But fitness got measured on a treadmill because that's what scales in a hospital. The training is the thing, the number is the receipt.
And your watch is guessing
A real VO2max test involves a mask, a metabolic cart and someone talking you into two more minutes. Your watch is inferring it from pace and heart rate, so a bad heart rate reading produces a bad estimate - if it's been cadence-locking on easy runs and reporting 178 for a jog, it'll conclude you're less fit than you are.
Mine went 44.2 to 61.3 in twelve months, flat from June to November and then nearly vertical in December, which is exactly when I started riding indoors with better data. And then this summer it plummeted to 55 while I was in the best aerobic shape of my life. Heat pushes heart rate up at any given pace, the watch reads that as slower for the effort, and down goes the estimate. Nothing about me changed except the weather.
And my current main goal is raising my VO2max
Which is funny after all of that. I'm targeting it specifically, with multimodal training, on purpose, as a vanity metric, and I know exactly what I just spent a thousand words arguing.
The defense, such as it is: chasing it across running and riding and the SkiErg rather than one sport means the training that raises a modality-specific number is just a broader aerobic base by another name. The number is the excuse and the training is the point, which is the same thing this whole piece has been saying, from the other side.
If you want something more useful to watch: same pace at a lower heart rate, or the same heart rate at a faster pace, over months.