your max is your max. if you hit 204 then that is your max.
i suggest an afternoon at your local track for some Max HR testing. warm up, then run 400 meters at a fair pace. rest 2 minutes and go again but a bit faster. do this four times or so with the last being an all out effort. the highest HR reading should be close to your max.
of course the only true way to determine you max is in a lab.