It changes more world-wide too. And yeah, it's garbage. It's really trying to put a magic number on life experiences so that people can be protected under the law, but it doesn't account for different life experiences or even that people mature both physically and mentally at different rates.
It's no problem. It's a tough topic when you've been living a somewhat normal life. I can't imagine what it'd be like having to catch up after seven years as a coyote.