The main point for me is that it is never: Oh she has such good metabolism and can eat whatever she wants. And this is what you hear from overweight people.

The truth is that healthy weight people were either brought up with the good eating habits, or they acquired them on their own (with the former being more likely IMO).

So the real question is: Can you acquire good eating habits (by this I mean genuine preference for healthy food) after a lifetime of eating crap or are these habits set in the early childhood and largely unchangeable?

I really truly prefer veggies to pizza, but my parents were feeding them to me since I was 6 months old. And from what I read so far, preferences for food are established early (even in fetus stage, fetuses learn to like what their pregnant mothers ate).