Recovery is so important and it is different for each individual. Finding the right combination of nutrition, exercise, stretching, yoga, sleep, etc. can be a bit of trial and error until you find what allows you to get back out there to hammer again at your 100%. I absolutely agree that age makes a ton of difference. It has for me in my early 40's compared to 20's and early 30's. I have a congenital heart... issue (won't call it a defect because it's bothersome, but not life-threatening, even working at VO2 Max) and otherwise I'm super healthy. But a slight electrolyte imbalance (low potassium) threw me into a tachycardia that wasn't particularly fast (120's - 150's... resting heart rate is low 50's, though) and not dangerous, but needed to be addressed with I.V. Potassium. It came on an hour after a 30 mile hard ride that was on the heels of rides that I didn't let myself adequately recover from. It was pointed out to me by my cardiologist that electrolyte drinks are NOT adequate, especially with regards to potassium (we looked at many different brands, including my favorite Scratch and they have next to no potassium at all). Supplements are not absorbed efficiently. Proper nutrition is key. The take away for me was... active recovery is good (take a day to do a fast-paced walk... no need to be sedentary to recover) and look at your diet. Supplements and electrolyte drinks help only a very small bit... get your body's needs from a healthy, well-balanced diet and listen to it when it needs to rest. Rest does not equal couch.
Good luck finding your right balance.
The bicycle has done more for the emancipation of women than anything else in the world. ~ Susan B. Anthony