Right thinking can be developed at any age. I knew some people who have children who thought their kids about generosity, quite effectively actually. So much so that when the little boy was six years old, there were 2 parents and two children, there were only 3 pieces of fruit left and so the mother said, "Oh I won't eat one, you all can have them." But the little six year old said, "No that's not right." And the mother did not understand, "What, you'll get one, don't worry." And then the little six year old went away from the table and brought a pencil and a piece of paper and started drawing 3 circles and lines through them. And then said, "Well, if you cut the fruit this way, then everybody can have an equal amount and none of us have to go without."
The parents tried to teach the kids about the interrelationship of life in nature. Obviously they did it very effectively, because one time they had to leave the kids with someone to go to another town. When they came back their friend said, "You're children are not normal." - "What do you mean?" - "Well, when I was outside in the garden one day, I went to pick the flowers in the tree and your three year old said, "No, please don't pick the flowers there, they are food for the birds and the bees. You can enjoy the flower without having to own it."
Anytime, it depends on how much you understand it, really, and how skillful you can bring it across to your children.