According to Erik Erikson, the identity crisis (the question "Who am I?") is of greatest concern to people of what age?

adolescents

Explanation:

The answer to that question will make anyone conscious of having an identity.

This is particularly important for teenagers:

Erikson notices that adolescents will commonly experience an identity crisis

Since the ego develops during this age, he noticed a series of stages of identity formation where much of social interactions and a constant sense of change happens as new experiences shape our identity with new information that is present in day to day interactions.

An adolescent will frequently find confusion to that question or find many doubts, and after having many experiences and social learning solve most of his crisis of this age.