system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why old monkeys don't have white fur?
gpt
Old apes do get gray, starting with their heads, just not to the extent that humans do. 

Why? Your hair follicles makes two chemicals to feed the hair: catalase and hydrogen peroxide. The catalase breaks down the hydrogen peroxide into water and oxygen*. When you stop producing catalase, you just have hydrogen peroxide, which bleaches the hair. The hair's not a gray color, it simply doesn't have any color anymore. 

For whatever reason, other great apes don't have the same wide-scale catalase loss that humans have. They do have other signs of aging, such as body hair loss, that we don't have.

**correction of mistake*