Push-ups are the main functions of pectoralis major and triceps brachii (muscles behind the upper arm). 17 years old, 45 years old is good enough. I can earn more than 100 at the age of 20, but when I am 17, it seems to be almost the same as you.

Any exercise needs to adjust breathing. You can inhale when you come down, and exhale when you lift it, deeper. After all, strenuous exercise consumes a lot of oxygen. Lack of oxygen can produce lactic acid, feel lack of oxygen and acid.