Louisiana became the 18th state of the U.S. on 30 April 1812.
The 18th U.S. President: Ulysses Simpson Grant (Republican, Ohio, 1869-1877).
The last (26th) amendment of the U.S. Constitution, ratified on 30 June 1971, changed the voting age from 21 to 18 years old.
U.S. men of age 18 through 25 must register with the Selective Service System, in case U.S. government needs rapid expansion of Armed Forces for national emergency.
A page can become a squire at the age of 14. A squire can become a knight at the age of 18 to 21.
The number of positions in the line of succession for the U.S. presidency, by the Presidential Succession Act, 1947: (1) Vice President, (2) Speaker of the House, (3) President Pro Tempore of the Senate, then the Secretaries of the 15 departments in this order (but no naturalized citizen is eligible for Presidency): (4) State, (5) Treasury, (6) Defense, (7) Justice (Attorney General), (8) Interior, (9) Agriculture, (10) Commerce, (11) Labor, (12) Health and Human Services, (13) Housing and Urban Development, (14) Transportation, (15) Energy, (16) Education, (17) Veterans’ Affairs and (18) Homeland Security, (which became the 15th U.S. President’s Cabinet-level department, on 25 November 2002. The first Secretary, Tom Ridge, sworn in 24 January 2003).
“Hồng Bàng”, the first dynasty in Vietnamese history, spread over 18 generations, called the Kings “Hùng”.
18 & 17
[History] The 18th U.S. President: Ulysses Simpson Grant (Republican, Ohio, 1869-1877).
His Vice Presidents were: Schuyler Colfax (Indiana, 1869-1873), the 17th U.S. Vice President and Henry Wilson (Massachusetts, 1873-1875), the 18th U.S. Vice President. There was no Vice President in the period 1875-1877.