When n=∞, this states that the homotopy category of infinite loop spaces is equivalent to the homotopy category of connective spectra; see The geometry of iterated loop spaces by May.
We can also prove this statement in the general case. Let X be a (pointed) n-connected space; then the loop space Ωn+1X is an En+1-space, and this is easily checked to be grouplike. So if nConnTop and An are the categories of n-connective spaces and En+1-spaces, respectively, then the (n+1)-fold loop space functor Ωn+1 induces an equivalence of categories between nConnTop and An. (I believe the statement for En+1-spaces in general should be somewhere in May's book; I can't find it, though.)
One implication of this, using the Freudenthal suspension theorem, is that if a homotopy n-type has the structure of a grouplike En+2-space, then it canonically has the structure of an E∞-space, which is a special case of the Baez-Dolan stablization hypothesis. (See here, for example.)
RE your edit: a connective spectrum is usually defined as an object of the homotopy limit of the sequence ...→Topn+1→Topn→...→Top1. (See also Denis's comment on your question.)