The question is whether or not you refer to axiomatic set theory, or naive set theory. If the former, then the answer is probably "after you've seen a bit of mathematics"; if you mean the latter then "right now" is probably the right answer.
In my undergrad studies, the naive set theory course was the perquisite for all other math courses (even those on the first semester, which you were obviously allowed to take in parallel).
In other universities a lot of the topics covered in that course (basic Boolean operations, relations, functions) would be covered in the first two-three weeks of calculus, or algebra, or they might have a course called discrete mathematics covering that.
On the other hand, axiomatic set theory requires to understand what does it mean to deal with an axiomatic theory. It is usually taught to people that already seen a bit of mathematics, and learned a few basic definitions from logic.
Axiomatic set theory, in its basic form anyway, fits better a third year undergrad course, rather than a freshman level course.