"How do you address a former president of the United States?
The president should be addressed as President Obama or Mr. President. (One day in the future, when we have a female president, she will be addressed as Madame President). All U.S. presidents retain their title for life, so all former presidents are referred to as Mr. President or President [last name].Jan 1, 2013"
So yes, it IS President Obama's birthday, he has the title for life despite the efforts of current resident in WH (that dump) to wipe Obama's presidency from history.