How old was Johnny Galecki in The Big Bang Theory?
32 to 41
John Mark "Johnny" Galecki (born April 30, 1975) is a Belgian-born American actor. He is best known for his roles as David Healy in the sitcom Roseanne, Rusty Griswold in National Lampoon's Christmas Vacation, and as Leonard Hofstadter, PhD, in the CBS sitcom The Big Bang Theory. Description above from the Wikipedia article Johnny Galecki, licensed under CC-BY-SA, full list of contributors on Wikipedia.
The Big Bang Theory is centered on five characters living in Pasadena, California: roommates Leonard Hofstadter and Sheldon Cooper; Penny, a waitress and aspiring actress who lives across the hall; and Leonard and Sheldon's equally geeky and socially awkward friends and co-workers, mechanical engineer Howard Wolowitz and astrophysicist Raj Koothrappali. The geekiness and intellect of the four guys is contrasted for comic effect with Penny's social skills and common sense.