Who was the first president born in the nineteenth century?
The first United States President born in the nineteenth century was Millard Fillmore, born on January 7, 1800. This answer assumes that you take the popular view of assuming the 19th century began in 1800, which would be true if you decide the first century lasted for only 99 years, but that does seem right to me. If you give the first century its full complement of 100 years, the 19th century began in 1801…
A man who was born in the 1st half of the century was x years old in the year x2 which year he was born?
John Adams, Thomas Jefferson, James Madison, James Monroe, John Quincy Adams, Andrew Jackson, Martin Van Buren, Williiam Henry Harrison, John Tyler, James Polk, Zachary Taylor, and James Buchanan were l born in the 18th century and died in the 19th. In addition, Millard Fillmore was born in 1800 which technically is the last year of the 18th century but is popularly considered to be in the 19th.