Mercury is the closest planet to the Sun, and so it's the fastest to orbit the Sun. In fact, Mercury only takes 88 days to orbit the Sun. In other words, Mercury's orbit only takes 24% as long as Earth's orbit. If you were born on Mercury, you would have celebrated 4 times as many birthdays as you do on Earth. In other words, if you're 10 here on Earth, you'd be 40 in Mercury years. Now that's a possible way to grow up more quickly.