My parents retired at 60 and lived another 30+ fulfilling years. I think the key is to still feel you are doing something beyond the fun stuff, and are contributing to your world. They delivered meals on wheels, fed many in their community from their large garden, and did other volunteer work.
My dad is an engineer... a thinking person. Retiring so young was, by his own admission, not good for him. Volunteering does not fulfill everyone in retirement. And contributing to the world comes in all forms. I'm glad your parents did well in retirement... not everyone does
Of course it’s not for everyone. Some find purpose and fulfillment in their careers. I think my folks were a bit burned out after almost forty years as teachers and were more than ready to move on. OTOH, my father in law was forced into early retirement and was miserable.