When did Tweeter started geo tagged tweets?



My current work with the API requires that I have an idea when approximately is the ‘first’ geo tagged tweet dated. When have you started the geolocation of tweets feature? What would be the month/year of the first (earliest) geotagged tweets? An answer like “There are certainly not geotagged tweets earlier than May 2013” would satisfy my answer.

Thank you,
Alexander Stefanov