I assume by feed you mean sexual feed? What would they eat from before that, then?<br/><br/>When my son was born, he ate more as an infant than he does now, at two. But, food is his primary energy source, so that might not be entirely comparable. Still, something that is trying or anticipates growing requires greater input, I don't think less. I don't see that as being feasible.<br/><br/>That said, I suppose we could have them dormant until they're old enough to feed, like some species of amphibian, some insects. But that would categorize them as non-mammalian, and they would only have things like breasts if they were in a human disguise, because they have no need to feed a living creature. I think, at that point, the breasts might serve as a feeding device. Biologically, there is little in terms of waste. A whole species isn't likely to have something they don't use unless they once did before.<br/><br/>So, they might have found a more efficient way, but if they have breasts, then by default, they had to have had a way to feed their children prior to feeding maturity.<br/><br/>So, maybe they breastfed until they started being able to feed of sexual energy, like an afterglow as Zaer said, before they could do it on their own? It would be like a baby breastfeeding until the mother makes puree, then it eats pre-cut food, and then eventually learns to drive to the damned store itself.