I agree that, for some people, it may be doable, at least for a while. I have trouble sustaining normal iron levels so I won't go back to being veg. Iron is typically a more common problem for women because of our menstrual cycles.
I don't think it's impossible to eat healthily on a vegetarian or vegan diet, but in my experience it's much more difficult to get all of the needed nutrients.
Congrats to you for staying at it for over 40 years, though!