There are only 21 million bitcoins that can ever be mined, regardless of the earths population and its corresponding demand for bitcoins. Once all 21 million have been mined, there will never be any new bitcoins (unless a change to the protocol is made to increase the supply). Roughly it has 17M bitcoins circulating. Though 21M is near still it is far enough to achieved the max supply. Lets just enjoy now since it havent reach its max supply.