I just had a trivia pop up and as you can see from my above screen shot I answered 6 years old which is the correct answer and it marked me as wrong, 5 is not the correct answer. I'd like my 175pt free play, thanks! The sources for the correct answer are below.
Correct answer source: https://en.wikipedia.org/wiki/Maria_Sharapova
"In 1993, at the age of six, Sharapova attended a tennis clinic in Moscow run by Martina Navratilova, who recommended professional training at the Nick Bollettieri Tennis Academy in Bradenton, Florida, which had previously trained players such as Andre Agassi, Monica Seles, and Anna Kournikova."
Correct answer source: http://www.imdb.com/name/nm1682495/bio
Maria started hitting tennis balls at the age of four. At the age of six, Maria Sharapova participated in a exhibition in Moscow that featured Martina Navratilova.