Just How Old Big Bang Theory Characters Were in Season 1?
When it comes to television, actors quite often play characters younger than themselves, and that's why it is sometimes difficult to tell a character's age when this detail isn't explicitly mentioned in the show.
Since The Big Bang Theory premiered so many years ago, it's almost impossible to recall what the characters looked like in different seasons, let alone remember their ages.
As the show continued and the plot lines became more complex, the characters' biographies got all the more twisted, and it's likely that any regular audience member wouldn't be able to say how old TBBT characters were when it all started.
Sheldon
From The Big Bang Theory itself and Young Sheldon, we learn that Sheldon was born in February 1980, as he's yet under 10 years old when the spin-off begins in the late 1980s. Season one of TBBT takes place in 2007, and Sheldon is 27 years old at the time, which makes him the oldest character among the nerds.
Leonard
Appearing along with Sheldon as his roommate in the very first episode of TBBT, Leonard is only a couple of months younger than Sheldon — he's also 27. In fact, Leonard's age is no secret because, later on the show, we learn that he's graduated from school and gone through all the stages of growing up just like any other person, without taking shortcuts like Sheldon.
Penny
A gulp of normality, Penny is the youngest character among the TBBT's main cast. Born in December 1985, Penny is around 21 or 22 years old in 2007 when the show begins.
Raj
Although he makes it to the regular characters only later on the show, Raj also appears in season one of TBBT. According to the plot, he was born in October 1981 in New Delhi, which makes him 26 years old at the beginning of the sitcom.
Howard
Unlike the other nerds on TBBT, Howard doesn't have a PhD, and we can't rely on his academic history to establish his age. But we do learn that, just like his best friend Raj, Howard was born in 1981. Yet a side character in TBBT's first season, he is also 26 when he appears on the show.