Categorical ideas should be certainly introduced early, as they are quite useful. On the other hand, as Andreas and Terry say, studying category theory at the beginning of your mathematical education is a waste of time, and could be a turnoff, like all unmotivated formalism.

On the other hand, the formal language of category theory should be learned, and used, at some point. I have seen several interesting papers written by very good mathematicians, containing theorems with statements like "It is the same to give a regular thingamabob over $X$, and a von Neuman whatchamacallit with a seminormal connection over $X'$". What these statements usually mean, is that there is an equivalence of the category of regular thingamabobs over $X$ and that of von Neuman whatchamacallits with a seminormal connection over $X'$; but they could also simply mean that there is a bijection of isomorphism classes, and to know which is true you have to study the proof. This means, I suppose, that the authors, who must have seen the language of category theory at a certain point, have not interiorized it, and don't have a feeling for when its use is appropriate.

In my opinion, the concept of equivalence of categories is a real turning point. Up to that point, one can probably get away without it (for example, universal properties, like that for the tensor product, are easily explained without the formal language); this is harder to do with equivalences. On the other hand, you don't see many examples of equivalences in the beginning of your mathematical studies. Maybe the first one is that between coverings of a space, with appropriate hypothesis, and sets on which its fundamental group acts. Stating the connection between these two classes of objects as an equivalence of categories clarifies things enormously; I wish someone had explained it to me when I was a student, instead of just telling me that there is a bijection between isomorphism classes of connected covers and conjugacy classes of subgroups, and other statements in this spirit, all descending very immediately from the "real" theorem, which is the existence of the equivalence.