What time period did the book "Ender Shadow" by Orson Scott Card take place in?

"The series is set in a future where mankind is facing annihilation by an aggressive alien society, an insect-like race known colloquially as "Buggers" but more formally as "Formics." The central character, Andrew "Ender" Wiggin, is one of the child soldiers trained at Battle School (and eventually Command School) to be the future leaders of the protection of Earth. The year is never specified, although the ages of the Wiggin's children are specified to change throughout space, also carefully taking in the relativity of space and time."