Simplify the following text for a Grade 9 native English-speaking person.
Original: In August 1914 , shortly after the outbreak of World War I , Ponticelli joined the 1st RÃ giment de Marche of the French Foreign Legion at 16 years old , lying about his age to do so .
Simplified: In August 1914 , after the start of World War I , Ponticelli joined the 1st RÃ giment de Marche of the French Foreign Legion at 16 years old .