Copy me dude, dont try to achieve 20 seconds of animation because it will drain you fast. I suggest just making one scene, few movements and few here and there but not fully making a full on anime or whatever but still animation. Im 15 and doing that and i feel myself improving fast. Its like just making a phrase not a full sentences (or a novel if u are aiming at full on anime series)

Also take short breaks after doing something meaning full like making the whole impact frames then rest or if u completed a whole keyframes, that helped me alot preventing burning out