Do I need to be fit, young and very athletic to learn Brazilian Jiu Jitsu?
No you don’t. Because the key to correct Gracie Brazilian Jiu Jitsu Self Defense learning is to use BODY MECHANICS and leverage; you do not need strength or agility to execute a technique. There is a say in Brazilian Jiu Jitsu: If you are using strength to apply a technique that means you do not know that technique.