It can be done fairly early, if you build your fleets to counter the specific FE, the ai is easily outmanouvered so you only have to face one fleet at a time, if you are lucky you can even catch them with the jumpdrive debuff. I find i usually take more casualties from their stations than their fleets.
It is important to remember they dont rebuild their fleets, so if you got the time to do it over several wars it becomes easier. Early 2300 is the earliest I have managed with some heavy snowballing through conquest.