The producer-director - who has previously had success with teen comedies like Superbad, Freaks and Geeks and Undeclared - tackles a married couple's mid-life crisis in his most recent movie.
In an interview with Time Out Chicago, Apatow said that his latest project is reflective of his own maturity.
"I'm 44 years old. I've written about high school, college," he recalled. "But most of my life isn't about that transition anymore."
Apatow continued: "So it's a challenge to explore other periods of your life. I still find nothing funnier than that period. That moment when you have to define yourself and grow up is hysterical because we're all such a mess in that moment.
"That's why there'll always be a lot of movies and television about 15- to 25-year-olds 'cause it's when you make the most mistakes."
This Is 40 stars Apatow's real-life wife Leslie Mann and their daughters along with friend Paul Rudd.
The film is now playing in the US and opens in the UK on February 14, 2013. Watch a trailer below: