33.5kg is a reasonable weight - perhaps just slightly on the heavy side, but whether or not it is a good weight for the dog depends very much on his height.
Even if you can't get a measurement, you can observe visually. A boxer of correct weight should have the last 2-3 sets of ribs visible (not poking out, but the outline clearly visible when he's just standing normally), with a defined waist/tummy tuck up. Think greyhound (muscles on skeleton), only not so extreme
If his physique is closer to labrador than greyhound, its a clear sign that the dog is overweight.