It is stated during the Observation Reel that parents David and Barbara Jeans (51 and 43 years old, respectively) are late-bloomers whom have been married for over 20 years, but didn't start having daughters until they were in their late 40s and 30s respectively.
Even though this is the TV series' premiere episode, the first to be filmed was "The Weston Family" that was filmed during the summer of 2004. This was filmed during the autumn of the same year.