How old were these men when they first entered the Oval Office in the White House? Well, George Washington didn't get to work in the Oval Office. It wasn't built yet. However, we know our 1st and 16th president because we celebrate Presidents' Day using these two men's pictures a lot. Just how old were they when they were president? Theodore Roosevelt is known as the youngest man to be president. Donald Trump is known as the oldest man to be president. 1. You will need to subtract the year they became president from the year they were born. REMEMBER, if you are stacking and subtracting using the standard method, you will need to be sure the bigger number is on top. 2. Try to show your work for at least two presidents. Add a page if you know how and need more room. 3. Write each president's age above their picture. Be sure to label the number using Years Old, or y/o.