Basically lung capacity decreases with age and peaks at 18-21yrs.
Training can maintain and reduce the amount being lost.
If you have been a couch potatoe from 18-38 you will be able to get fit but compared to someone who has kept their lung capacity as high as possible who can exchange gas at a higher rate than you then you will have to work harder to keep up or stick a pump in his spokes!
Therefore ageing sucks. My 6.5 litres is now 5.5 litres 😥
But then again I know 55 yr olds are super skinny and race fit on single speeds.
You can increase vascularity but so can younger fitter people.
Don’t forget the science journals you read about sport science are 4 yrs out of date and teams using and developing the latest ideas are top secret unless you have worked in a sports science field and top teams.