How old was his “great uncle” in 1945? 50 or 60?
Only if he's somewhere between 110 and 120 years old today.
Barack was born in 1961. His mother, Ann Dunham, was born in 1942. Her mother, Madelyn Dunham (née Payne) was born in 1922, making her 19 at the time of the attack on Pearl Harbor.
According to a DUmmy citing a geneology site, Charlie Payne was born in Kansas around 1924, making him 17 at the time of Pearl Harbor.