Simplify the following text for a Grade 9 native English-speaking person.
Original: On August 25 , 1930 he set the round-trip transcontinental air speed record for pilots under the age of twenty-one years in his Cessna using a Warner Scarab engine .
Simplified: On August 25 , 1930 he set the round-trip transcontinental air speed record for pilots under the age of twenty-one years in his airplane .