Maybe it was more the novelty of having retired early had worn off, you were all excited about being able to go cycling whenever you wanted after retiring. Then by covid and all the doom and gloom during that period you started to focus on safety and health etc and the novelty of going cycling everyday had worn off.Before Covid I never felt my age, I was doing things that any young to middle age person does like cycling up mountains that would bend your bones and descending them like a bat out of hell, got really fit during Covid where I was contesting some Strava KOM's with the whippersnappers of the day
Then one day in 2023 it all came to an end when I started to question my safety out there and why I was doing it and that was it, haven't cycled since and that's also when the ageing started
You are only approaching 60 that is not old, it could be that you have too much time to reflect on these things which you wouldn't have if you were still working. You would have to make yourself goto work whether you wanted to or not.