I finally got the time to update my Longest reigns (current monarchs) website tonight, following the abdication of King Albert II and the swearing in of King Philippe of the Belgians two days ago. The change of king only meant that the Belgian king was moved from place no. 12 to 30, while the king of Lesotho and the monarchs in the line behind him was moved one step up.
King Bhumibol of Thailand tops the list, as he succeeded to the throne already in 1946. He is not the oldest monarch of the world, however, as King Abdullah of Saudi Arabia, b. 1923 or 1924, holds that position. The youngest monarch, as mentioned last time the Longest reigns website was updated, is the Emir of Qatar, Sheik Tamim, b. 3 July 1980.