NEW YORK (MainStreet) — Some websites may need to rethink their video advertising strategy.

A survey from Poll Position, a research group, finds that just 19% of Internet users think it is acceptable to watch an advertisement that is 30 seconds or longer in order to view free content afterwards, while the majority of those surveyed (54%) said the ads should last 15 seconds or less.

Younger viewers seem to have even less tolerance for longer advertisements. Just 12.5% of users ages 18-29 thought it was acceptable to sit through an online video ad that was 30 seconds or longer, whereas a quarter of those in the 45-64 age bracket said it was acceptable.

While the survey doesn’t offer an explanation for this age gap, our assumption is that it has at least something to do with older viewers being more accustomed to sitting through eight minutes of advertisements to watch a 30-minute show on television, whereas younger viewers grew up in the age of DVRs and TiVo, which allow viewers to fast forward through the commercials.

This subtle difference in how much ad time younger viewers can tolerate could prove troubling for news and video sites, as they risk turning off this valuable demographic by turning on too many ads.

Seth Fiegerman is a staff reporter for MainStreet. You can reach him by e-mail at seth.fiegerman@thestreet.com, or follow him on Twitter @sfiegerman.