Hello. Your boyfriend, height 165cm, standard weight 65kg, ideal weight (figure 58.5kg). If he starts working out. It is suggested that his weight should be controlled between 55 and 58.5 kilograms. Fitness is also a long-term project that must be adhered to. Otherwise, it is best not to choose fitness (if you stop halfway). The phenomenon of being out of shape is much more serious than the situation of weight rebound. As for when you can develop abdominal muscles, you need your own body (talent) and the degree of daily training. If it is a piece of fitness material. Abdominal muscles should develop well within three to six months. I wish you all the best, health, happiness and happiness. Please adopt it. Thank you.