In their darkest moments, people occasionally say “my best years are behind me.” The problem is, people say this whether they’re 69 or 29. Ezekiel Emanuel, a doctor and bioethicist, believes he only has 18 good years left: By 75, he wrote, “I will have made whatever contributions, important or not, I am going to make.”

At what age do we really peak? Is there ever a point where, intellectually, we’re as good as we’re going to get?

It depends on what you’re measuring, it turns out. In a study just out in Psychological Science, Joshua Hartshorne of the Massachusetts Institute of Technology and Laura Germine of Harvard take a look at the ages at which various types of cognitive performance crest. For the study, they gave 2,450 Americans of various ages and geographic provenances a set of 15 tasks, including math tests, picture completion, vocabulary quizzes, and even tapping sets of cubes in a certain order.

They found that most of the skills peaked in the subjects’ late teens and early 20s. Notably, though, four types of proficiencies didn’t fully ripen until people were in their 50s: vocabulary, math, general knowledge, and comprehension (a test that involved explaining why things are the way they are—for example, why we have a parole system):