Eating Habits/Selection

Another one for you wonderful people!

At what point in a childs life do they go from “eating the best first”, to “saving the best till last”.
What i mean is-
You give my a small child a plate of chicken nuggets and veggies- i guarantee you they will eat what he likes best, first (the nuggets, obviously!). Same goes for lollies- you give him a few lollies, he will eat what he considers the best first.
Now you give say a 13 year old (or heck, a 21 year old!) a plate of vegies and nuggets. Assuming they like nuggets and not vegies- chances are they will eat the vegies first, in order to “save the best till last”. Or they eat all the crappy lollies first- and save their favourites until the end.
WHY? At what point in our lives do we decide that its better to get the worst of something over and done with first, rather than previously when we enjoyed the best first?

I don’t think there’s a certain age. I had one son who, as far as I can remember, always saved the best till last. The other two didn’t, and don’t (one’s 22, one’s 8).