I would say for someone of your age start of with some bodyweight exercises and plenty of core work. Doing this will help you to prepare your body for when you do start a resistance programme. When you do start using weights get someone to teach you proper technique before you start trying to lift any serious weight. Learn the technique on large compound exercises such as squats, deadlifts, bent over rows, clean and presses, high pulls, chin ups etc.
Below are some bodyweight exercises you could start with.
Upperbody: Press ups, close hand press ups, tricep dips, chin ups
Lowerbody: Squats, single leg squats, side lunges, step ups, reverse lunge, jump lunges, jump squats
Core: Plank, side plank, floor bridges, crunches, leg raises, oblique twists
Cardio: Burpees, squat thrusts,jacks, vertical jumps.
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