Barack Obama was 47 years old when he took office as the 44th president of the United States on January 20, 2009.
To provide some context, Obama was born on August 4, 1961. This means he completed his 47th year on his birthday in 2008, just a few months before he was inaugurated. His age at the time of taking office was notable as he was one of the younger presidents in American history, highlighting the theme of change and a new generation of leadership that he campaigned on.