All that stuff you list makes you slower, age the least.

Minimizing getting slower with age is really kinda simple. Causes: weight gain, muscle loss, VO2max loss, slower recovery.

Weight gain: lose weight, duh. We know we'll lose power as we age. To keep the watts/kg up, weigh less than you did when your watts were higher.

Muscle loss: work out! Ski, lift weights, backpack. Stress your legs on the bike, too. Stand for long periods, push huge gears sometimes.

VO2max loss: Train smarter. The science of training keeps advancing. Keep up with it.

Slower recovery: Eat smarter. Use supplements. Nutritional science keeps advancing, too.

At 71, I did a 100+'/mile training ride with friends a couple months ago. I was climbing at about the same VAM that I did 15 years ago. These were short climbs, though, no more than 1000' each. I'm noticeably slower on the 3000' climbs. But basically I've simply been following my own advice, as above.

I had a horrible RAMROD this year. I was 14th oldest out of 800 and only finished 221st, when I should have been ~100 places faster. And I've always had a crappy VO2max, struggling to do an 8' mile. I did ~5000' of the climbing in a 26/27 gear. Knowing how to ride goes a long way. I'm going to kill it next year! Arrrggh!