system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:How does your body decide when it is time to start puberty?

I undestand that puberty is caused by hormones like testosterone and estrogen, but what causes these hormones to be released? Does your body measure time and decide to release testosterone after a certain amount of time?
gpt
Adequate levels of leptin, released by fat, causes the hypothalamus in the brain to release gonadotropin-releasing hormone. This hormone causes the pituitary gland in the brain to release follicle stimulating hormone and luteinizing hormone. 

Both of these work in the testes/ovaries to begin sexual maturation and production/maturation of sperm and egg cells, and the release of sex hormones like estrogen, testosterone, progesterone, etc.

So basically, your body does monitor its own growth to decide when to start the process of puberty.