What determines the frequency range of a current transformer?
The lower frequency limit is defined by how many volt-seconds the core can handle without saturating out. Generally, the smaller the core, the higher the minimum frequency, since a higher frequency means smaller on-time and lower volt-seconds for the transformer to deal with.

(Most CTs use ferrite cores, so if there isn't a specified \$ B_{max} \$ you can try 0.22T and figure out what volt-second product you can achieve with your specified burden resistor.)