I’m not a physical therapist, but I’m convinced that grueling training in the hopes of getting big biceps is more likely to deplete the teenage body. You need to consult with a specialist or find ready-made workouts for teens that are approved by experts in physiology and anatomy. I can only advise you to pay attention to those home workouts where there is more strength training. By the way, you don't need to buy bulky and expensive sports equipment like in a gym. You can get good results if you use the
resistance bands set, for example, to pump strength and endurance.