One of the major themes of The Big Bang Theory is growing older and maturing. Big Bang spans twelve years in-universe and out. Viewers follow the main characters through every facet of their lives as they develop their relationships, their careers, and their families.
Following the custom of this type of sitcom, viewers are introduced to The Big Bang Theory's characters at a fairly young age, and the show follows them as they age in real time. The characters are all at different stages of development and their careers. Even those who are introduced later in the show grow and change significantly by the time of the finale.
Updated on April 21st, 2023 by Casey Coates: This list has been updated to reflect CBR's current publishing style.
Leonard Hofstadter
27 in the pilot, 38 in the finale
The de-facto protagonist, Leonard Hofstadter, is 27 in The Big Bang Theory's very first episode. Despite being one of the older members of the group, Leonard is actually improbably young to be in the infancy of his career. He is said to have received his PhD at 24, rather than the typical 26-30.
- Born May 17, 1980
With this prodigious feat, Leonard is at the beginning of his career in Big Bang's pilot. Over the course of nearly 12 years, he ends Big Bang at 38. In this time, he manages to develop social skills, be part of several significant scientific expeditions, co-author several papers, get married, and father a child. He ends Big Bang one of the most well-rounded characters, though many fans felt he'd lost his charm.
Raj Koothrappali
25 in the pilot, 37 in the finale
At just 25 in the pilot, Raj Koothrappali is the youngest of the four main characters in The Big Bang Theory. Despite his young age, he has managed an impressive education innings, graduating with a PhD from the prestigious Cambridge University and being settled into his career.
- Born October 6, 1981
Aged 37 in the finale, Raj has one of the more volatile careers. After working as a research astrophysicist - earning some fame and a mention in People magazine - Raj's work ends. He becomes a research partner with Sheldon to avoid his visa expiring. Later still, he becomes a speaker at the Planetarium. He is the only main cast member to still be single at Big Bang's end - despite attending the Nobel Prize ceremony with Sarah Michelle Gellar.
Stuart Bloom
34 in his first appearance, 45 in the finale
Stuart's status as a main/recurring cast member changed often over the course of The Big Bang Theory. By the final season, he had been considered a main cast member for some years, receiving opening credits and getting his own storylines and character arcs.
- Born May 7, 1974
When he was first introduced in Season 2, Stuart is 34, the oldest member of the cast. Like many of the characters in The Big Bang Theory, Stuart struggles throughout his mid 30s. He bounces back towards the middle of his 40s, with his comic book store increasing in popularity, and eventually starting a relationship with his assistant manager, Denise.
Bernadette Rostenkowski
25/26 in her first appearence, 35/36 in the finale
Bernadette Rostenkowski's exact age and birthday are not known, only that she was born at some point in 1984. Initially, she is either 25 or 26. She did not appear until almost three years into Big Bang.
- Born 1984
By the time of Big Bang's finale, Bernadette is either 35 or 36. She develops a great deal, beginning as a PhD student working at the Cheesecake Factory. Before long, she earns her doctorate and accepts a job at pharmaceutical corporation ZanGen. She becomes one of the most financially-successful members of the group. In addition, she marries and has two children, raising them while working.
Howard Wolowitz
25/26 in the pilot, 37/38 in the finale
Howard Wolowitz's exact age and birthday aren't ever stated, but he was born sometime in 1981, making him older than Raj. He begins Big Bang with his Master's degree and settled in engineering.
- Born sometime between March 1 and September 30, 1981
Howard begins as the most immature character, being lecherous and borderline predatory. By the end of the show, he gets married and becomes a father to two children, never losing his sense of humor. He worked on the Mars Rover, developed secret government projects, and became an astronaut, all before the age of 37.
Amy Farrah Fowler
30 in her first appearance, 40 in the finale
Introduced in the third season finale, Amy Farrah Fowler is the second-oldest of the main characters at the age of 30. She begins Big Bang well-regarded as a neuroscientist, and this increases with invitations to conferences and fellowships.
- Born December 17th, 1979
Amy ultimately wins a Nobel Prize in Physics and becomes one of the cast's most-renowned scientists. She also develops in her personal life, learning to manage her relationship with Sheldon.
Sheldon Cooper
27 in the pilot, 39 in the finale
Unlike many of the others, Sheldon's unusually young age relative to his advanced career is given an explanation. Througought The Big Bang Theory, Sheldon is consistently described as a prodigy. He is said to have graduated high school at 11 and college at 14, and received his PhD at 16 before working on a second dissertation.
- Born February 26, 1980
Sheldon is the most-advanced in his career, having spent seven years working at Caltec. He undergoes immense personal growth by The Big Bang Theory's finale, becoming much more socially adjusted and learning to enjoy a romantic relationship with Amy. Endearing fans with his quotable lines, Sheldon undergoes several changes that culminate in him winning a Nobel Prize in Physics with Amy at the age of 39.
Penny Teller
21 in the pilot, 33 in the finale
Penny Teller is by far the youngest of the cast of The Big Bang Theory. She moves to Pasadena at the beginning of her acting career, working at the Cheesecake Factory to make ends meet.
- Born December 2, 1985
Over the course of Big Bang, Penny abandons her dream of acting for a well-paying job as a salesperson for ZanGen, where she becomes the head of a sales team. Penny's personal development leaves her well-adjusted to committed relationships and starting a family. With nearly 6 years between them, she and Leonard have the largest age gap of any couple in the cast by the time they get together in the finale.