Barack Hussein Obama was born of August 4th, 1961. At the time of his election and inauguration as 44th President of the United States he is 47 years old. He is the fifth youngest President of the United States. The youngest president to serve was Theodore Roosevelt, who was 42 years old when he was sworn in. The youngest president elected was John F. Kennedy, who was 43 years old at the time of his inauguration. Roosevelt was sworn in after the assassination of William McKinley in 1901, making Kennedy the youngest president actually voted to the office. At 69, Ronald Reagan was the oldest president to take office.