Hahahahha, yes, I do weigh considerably more now than I did at age 12. Wish I didn't. What is aikido? That sounds like something I should look into.
It's astounding to see the films of a diminutive, elderly Ueshiba manhandling young aggressive men twice his size - without seeming to exert himself at all.
But because there's all this throwing and flying through the air, the first thing students learn is how to fall - you learn to tuck and roll and to maintain balance while falling - and to distribute the impact over your body so that you don't just land and stop like a bag full of bricks.