Without proper training (i.e., taking care of all the stuff that is not Volleyball but supports you playing it, like back muscles, shoulder mobility and stabili

Without proper training (i.e., taking care of all the stuff that is not Volleyball but supports you playing it, like back muscles, shoulder mobility and stability, stretching, school), it is certainly not healthy at a certain level/age. Otoh, playing five hours of volleyball alone a week is not that much if the level is not too demanding.