There are a zillion different opinions on this. IME, if your legs hurt while you're on the bike, you're protein deficient. Studies have been done on endurance athletes which show they need up to 1.7g/kg/day. I'm an ovo/lacto/pisco vegetarian who eats very little fish. It's been my practice for over 20 years to supplement with 15g of whey protein 4 X day, usually just before meals and at bedtime. I might add a 25g bolus right after a particularly hard or exhausting workout. Works for me, but perhaps other regimens might work better. I ran across one study which found optimum recovery using 20g of whey protein isolate every 3 hours for 12 hours following a hard workout.
Here's a good primer on masters nutrition:
https://www.hhs.gov/sites/default/fi...ate_health.pdf
Here's an article on protein quantity:
https://www.hammernutrition.com.au/k...-much-protein/ Ignore the product pushing and just look at the numbers and timing.
There's little scientific evidence for establishing protein requirements for endurance athletes our age simply because there are so few of us. We have to go on anecdotal evidence.
I disagree that cycling doesn't strengthen the legs. I can not enter my gym for a month and still squat 1.4 X bodyweight. Of course I ride my guts out every weekend.
There's also disagreement about strength training and whether that improves cycling performance, but perhaps that's beside the point. At my age, I'm pretty sure it does, sure enough to do a good bit of it from October-June. There's a good (IMO) thread about strength training for cyclists here:
https://www.bikeforums.net/training-...e-athlete.html
Another thing which I do for overall health and strength is hiking in the mountains once a week, weather permitting. My wife and I hike the day after the week's hard group ride, usually on our tandem. Helps.
At 74, I'm having a pretty good season. This past Saturday I managed 2000'/hour on a 1500' climb that started at mile 60 on a long ride. I was pleased to say the least.