Michael Rosenbaum, the actor who portrayed Lex Luthor in Smallville, was born on July 11, 1972. The series Smallville aired from 2001 to 2011. Therefore, to determine Rosenbaum’s age during Smallville, we can calculate it based on the years of the show’s production.
If we consider the entire run of Smallville, Rosenbaum would have been between the ages of 29 and 39. However, it’s worth noting that the character of Lex Luthor was depicted at different stages of his life throughout the series, so Rosenbaum’s age may have varied depending on the specific season or storyline being portrayed.