It's more depressing to contemplate old age than to actually reach that serene state. Witness legendary US elder statesman Bernard Baruch, who at 81 told Newsweek: "To me old age is always fifteen years older than I am."

Nonetheless, TV network NBC will this morning be examining the mirror for telltale grey hairs and crowsfeet.

The cause of its preoccupation is a report on TV viewing trends published Thursday by Magna Global USA. According to this study, over 45% of NBC's primetime audience now comprises adults aged fifty and over - gloomy news for a network that has traditionally delivered the coveted 18-49 demographic

The median age of NBC's audience has risen since the 2003-04 season, from almost 46 years to 48 this season, says Magna. Median age is a relatively recent - but increasingly significant - measure of a network's advertising appeal.

CBS, with an audience median age of 51.8 years, is even more venerable than NBC and will be cautiously flexing its joints for sounds of creaks.

But the Viacom-owned unit can console itself with the knowledge that it has actually grown younger since the 2003-04 season when it reached the ripe old [median] age of 53.

Magna Global, an offshoot of Interpublic Group, charts the declining years of the 'Big Six' networks:

CBS: 51.8
NBC: 48
ABC: 45.3
Fox: 38
WB: 35
UPN: 32.9

Explains Magna Global evp of audience analysis Steve Sternberg: "Median age is not a replacement for other types of measures, but it enables you - with a single number - to get general trends."

The median age of all US TV households is 37.9.

Data sourced from AdAge (USA); additional content by WARC staff