Given a diet of US imports such as Gossip Girl, Friends, and Lost you'd be forgiven for thinking that most American television viewers were about 20. But figures this week have revealed that the average age of those watching TV in the US has tipped 50 for the first time.

A study of the big five broadcast networks from research firm Magna Global shows that the average viewer no longer falls within the coveted 18–49 demographic so sought after by advertisers. The median age of the population in the US is 38. For the 2007/08 seasons CBS attracted an average age of 54, ABC pulled in the 50-year-olds, NBC managed 49, Fox's viewers were a younger-still 44 and The CW (which airs Gossip Girl and Smallville) comes out at 34. If you factor in viewings on DVRs, the average age drops by a year in most cases, though that is still higher than it's ever been.

The youngest show on CBS was Big Brother (45) while the oldest was news and investigations flagship 60 Minutes (60). ABC varied from UK import Supernanny (41), to police drama Women's Murder Club (57); Fox swung from Family Guy and American Dad (29) to legal drama Canterbury's Law; and The CW from teen drama One Tree Hill (26) to family drama Life Is Wild (45). NBC's youngest-viewing show was Scrubs (34) and its oldest was the detective show Monk (58).