While restaurant servers should undoubtedly be indiscriminate about their guests even before approaching the table, new research shows you can’t really fault them for wanting to wait on older diners.

Younger Americans are more likely than older ones to leave less-than-average tips, according to a recent Michelin study conducted by Harris Interactive. In fact, 30 percent of Americans age 18-34 reported that they usually tip less than 15 percent for good service. Hate to see what those folks would tip for bad service.

Of the “more experienced” diners polled, those ages 35 and up, only 16 percent said they regularly tip 15 percent or less for good service.

Overall, a surprising one-in-five Americans (20 percent) reported regularly tipping less than 15 percent for good service.

The survey of 2,019 adults was conducted online and results highlighted an interesting geographic breakdown of diners. Residents in the Northeastern U.S. are apparently the most generous, with only 15 percent of them saying they regularly tip less than 15 percent. Twenty-two percent of Southerners and 24 percent of Westerners say they regularly tip less than 15 percent for good service.

Parents, perhaps because they are always shelling out money for their kids, reported tipping less than 15 percent more often than those without kids. Twenty-seven percent of parents responded that they regularly tip less than 15 percent, compared with 18 percent of those without children.

Despite the averages, your servers might be enticed to fight for the tables with younger diners once they learn young Americans are prone to occasionally shell out the big bucks. The Michelin study shows younger adults are more likely than older ones to step out of their comfort zone and reward excellent service with a large tip.

Thirty-eight percent of Americans 44 or younger responded they have left a tip greater than 30 percent, compared to only 22 percent of Americans aged 55 and up. Sixteen percent of diners aged 18-44 said they have left a tip of 50 percent or more, while only 7 percent of those aged 55 and up have been so generous.

About 1-in-10 Americans have tipped 50 percent or more after a dining experience.

So while more young adults tip less, on occasion they’ve been known to go above and beyond.

The average American will go up to about 27 percent to reward excellent service, according to the study.

When it comes to the battle of the sexes, the research found that men and women, on average, usually tip pretty evenly. One outlier was the fact that men are more often willing to go above and beyond, as 39 percent of men reported tipping 30 percent or more on occasion, compared to 24 percent of women. Sixteen percent of men said they’ve given a tip of 50 percent or more, compared to 8 percent of women.

The Michelin study focused solely on tipping practices after above-satisfactory service. It would be interesting to see the demographic differences surrounding tipping after what guests perceived to be poor service.

Of course, many other factors beyond level of service weigh into the size of a tip. Past research from Cornell University shows other factors influencing tip percentage include the size of the dining party, whether the customer pays by credit card and even the sex of the server. Cornell’s research showed men left larger tips than women in cases where the server was female, and women tipped more than men when served by a male.