English - Does it include or exclude 16-year-olds?

My brother's friend is planning a trip and trying to calculate the costs. There's a discount for "children under sixteen years". Her little sister is exactly sixteen and she wants to know whether the sister gets the discount. I'm assuming she won't, but they wanted me to make sure.

Does it mean you have to be fifteen or younger to get the discount?


ETA: Okay, two people have already confirmed my belief that it means fifteen or younger and there have been no one saying otherwise. I think I'll believe them. Although if someone knows of a situation where "under sixteen years" also included 16-year-olds, I would like to hear of it.