In fact, none of these dates seem to have any particular relevance. The company's own history lists its incorporation date in 1998 - the nearest thing to a corporate birthday - as September 4.
And the idea for Google began years earlier in 1996, as a research project at Stanford University, when Page and Brin had a new idea for a search engine that would rank pages by how many other sites linked to it, rather than the crude format others used at the time - ranking them by how often the search term appeared on the page.
Google has celebrated its birthday with a Doodle every year since its fourth birthday in 2002. However, the first Doodle, for the Burning Man festival in 1998, actually occurred before the company was technically founded.
Last year, the company split under a new corporate umbrella,Alphabet, which hived off more outlandish divisions of the company such as its driverless cars unit and robotics subsidiary Boston Dynamics. The change saw its founders move away from Google’s day-to-day running.
18 years after it was founded at Stanford University, Google is one of the world's most powerful companies. It is second only to Apple in value, with a market capitalisation of $541bn (£417bn).
Page and Brin are ranked 12th and 13th on Forbes' list of the richest people in the world, with net worths of $35.2bn and $34.4bn respectively.