Timeline of Events that Happened Before the Show

This chronology is a timeline of events that happened before the show began.

1980s

 * February 26 1980: Sheldon is born
 * May 1980: Leonard is born
 * March-September 1981: Howard is born
 * October 6 1981: Raj is born
 * November-December 1985: Penny is born
 * Between 1980 and 1989: Bernadette and Amy are born
 * 1986-1987: Leonard, six years old at the time, walks in on his naked parents and his mother is swatting his father with Leonard's new ping-pong paddle

1990s

 * 1991: Sheldon starts college at age 11
 * 1994: Sheldon graduates from college at age 14
 * 1994: Sheldon's father dies
 * 1997-1998: Penny rebuilds a tractor engine all by herself at age 12

2000s

 * 2000: Amy begins training in the field of neurobiology
 * 2003: Sheldon and Leonard meet for the first time