Context of the meme:

What he's gonna do, is going to beat his meat

And if u dont know whats beating meat is masturbation,

Masturbate, as in He was always beating the meat. This term, considered vulgar slang, is used for males, since it uses meat in the sense of “penis,” a usage dating from the late 1500s.

And when boys enter puberty, the penis and testicles grow and the scrotum gradually becomes darker (read more about penis health) pubic hair becomes thicker and curlier. underarm hair starts to grow. boys start to sweat more, so boys beat their meat during puberty sometimes lol