DoyleG
Reality sucks, Princesses!
Nielsen's Total Audience Report from last year.
18-34 2:17
35-49 4:08
50-64 6:11
65+ 7:24
Nielsen of course tracks only actual television, not something like YouTube. I do think you're right that overall screen time is balanced out in a variety of ways. The key, of course, is that YT and various other media have a completely different viewing and revenue dynamic than television.
Ratings only measure what is being watched, not if people are sitting down and watching it.
Older people will leave the TV on during the day on specific channels as a bit of background noise. You see this in doctor's offices, dentists, and in workplaces that have public TV sets running.
Ratings systems still haven't developed an effective system to correctly calculate DVR usage as well.