After reading the study, a more accurate title for this would be, 'People who watch NBC, ABC and CBS and don't use DVRs are older than ever'.

When they included DVRs the average age dropped and the viewer age of the cable channels is considerably younger, even dropping in some cases.

You note, "Part of the jump is because of the introduction of the web and DVRs."

Well, only partly according to the article -
"... broadcasters began to greatly age themselves a decade ago as they mostly got out of the kids and teens business. With few shows at the major broadcasters targeted at that aud, save reality competitions like "American Idol," those viewers fled."

And given the study's focus on "live" viewing, it's not surprising that a shift would be seen in younger audiences with busier, more active lifestyles with the introduction of additional ways to make time shifting easy and convenient.

Some of this is demographics...as the population ages there are fewer young people. Also boomers were the first generation to grow up with TV so they gravitate to it not unlike how my father and the WWII generation still listened to a lot of radio. Gen-X and Gen-Y grew up with the Internet so it is their first inclination.

I think that the people who are older that watch TV still watch today's shows as well as reruns of classic shows they grew up with on cable networks like TV Land. The DVR and the web have taken some of that audience that leads to this older age average. When those devices weren't around, that's when you had the younger age average. Or there are people that don't watch a lot of TV because of their jobs and other commitments. It's really changed since last year.