How can the Earth be over billions of years old and were only in 2017?

The Earth has been around for approximately 4.6 billions of years. Humans first evolved from I believe apes around 5 million years ago, with Homo Sapiens evolving around 2 million years ago or so. The current calendar system we use today, the Gregorian system (in most western nations like America) marks the year 0 as the year Jesus Christ was born, not when the Earth was formed. Years before Jesus' birth are marked as B. C., with the numbers getting higher the earlier you go. In the Japanese system, the year is marked by how long the current Emperor has been in power, making the current year (2017) Heisei 29 in traditional Japanese calendars.