I am son of a king.
I saw my first action at the age of 12
I achieved the highest rank in the army of my king.
I wrote an essay on the art of war.
Who am I ?
Probably not right, but I have to post this answer.
Frederick the Great, King of Prussia?
That's funny Jeff. Damn funny
Maurice de Saxe, Marshal of France. He was one of the three hundred-odd illegitimate children of Augustus the Strong (!), Elector of Saxony and King of Poland. At twelve he was on the staff of Prince Eugene of Savoy at a couple of sieges and the Battle of Malplaquet. At the age of 17 he commanded a Saxon regiment, and at the age of 24 he took service with the French army of Louis XV. His ability and nerve made him a field marshal, and his most notable victory was the defeat of the Duke of Cumberland at Fontenoy.
His personal life resembled his father's; he could straighten a horseshoe with his bare hands to amuse guests, and his death certificate gave the cause as "an excess of women".
He wrote a commentary on warfare as practiced in the first half of the eighteenth century,
Mes Réveries, available online in English at
http://www.bellum.nu/literature/desaxe001.html
Was he a Mahoma's follower ?
DUUUUUUUUUUDE, death by sex.........might have to consider him my new hero!
Maurice de Saxe, Marshal of France.
That's correct! 
Congratulations!
Only six men became "Maréchal général des camps et armées du roi" (his full title). Only six men received that title in France. 5 before the Revolution (including Maurice de Saxe) and 1 after the second restauration: Nicolas Soult. 
Congrats and welcome to the Trivia Games.