I have found that as I got older, I turned more and more to including vegetables and fruit in my diet, but I will never ever be anything less than an omnivore. It's just that when I was younger, my diet was more heavily concentrated on meats.
Why has growing old evoked the shift toward more vegetables and fruits? I don't have an answer. I believe simply that my body has felt more comfortable consuming less meats. Is that possible? Truly. And it is a realization of that fact which has caused the shift.
I don't think that I would be more comfortable being totally vegan. I have to have meat in my diet.