The average ages at which an individual displays certain abilities are known as
a.
developmental norms
b.
process of maturation
c.
percentile
d.
proximodistal trend

A is the correct answer. The developmental norms are stages at which humans typically develop the ability to successfully complete an activity without aid, for example, being able to walk. When people have reached the age of the norm and cannot complete the activity, there may be cause for concern.