Do you put one space or two spaces after a period, and how old are you?

My daughter is applying to college and this article came across my field of view. It shows that parents (old) use two spaces after a period, and kids (young) use one space after a period, and it’s a way for admissions people to glean who wrote the essay. You will notice that I am using two spaces. One space feels wierd to me. My daughter uses one space.