Can We Say No Lack of Self-Esteem Here?

Joseph and Caleb were tossing a mini Nerf football back and forth. According to Joseph, he was finding it challenging to not throw it over Caleb's head and Caleb's tosses kept landing just short of Joseph. I was a little ways away in the dog park with Abe but what I overheard went something like this:

Caleb: "My throws are better than yours because my arms are stronger."

Joseph: "Oh really?"

Caleb: "Yeah, because your muscles are all old and used up. Because you use them for work and stuff. My muscles are young and so they are FRESH and so that's why I'm able to throw it faster and further."