Some people recommend martial arts, and these can be great but a disparity of size, age, and more make this unworkable.
Here is footage of O’Sensei, Morihei Ueshiba. He founded the art of Aikido, which I studied and was made mainstream by Steven Segal. For his sparring partners, he would only use 9th or 10th dan practitioners and would often oppose them while kneeling. His last public demonstration was in 1967, at the age of 83. On his deathbed a couple years later, he reportedly threw his most advanced student to the floor as a final lesson..
This footage might be a little zenny for some folks, but O’Sensei is almost 80 in this footage. If anyone thinks these guys aren’t trying, then you don’t know what you’re talking about, nor have you ever studied Aikido.
My father gave me a book of his on Judo. In it, the story is retold about a match that took place during the 1950’s in Japan. The Japanese Judo Champion vs an American Wrestling Champion. The American stood quite a bit taller than the Japanese master, and weighed almost 100 pounds more than him. The match ended in a draw.
It takes 5 years of study just to earn your 1st dan black belt in Aikido. And you never consider yourself a master – the black belt only means you are a serious student. As far as the whole immoveable object thing, when I achieved 2nd dan (as far as I ever went), we had some visitors, to include one of those 90lb females. “No contest”, I thought. I ended up face down, sucking chalk dust off the mat thanks to the humiliating lesson she taught me. My own hubris defeated me before I even started…
The wicked flee when none pursueth..." - Proverbs 28:1