Correct answer: "by age 2"
Most kids at age 2 ends having a difuse knowledge of themselves and starts to detach from their mothers. At this age they start to build their identity: who they are and who they believe they are. This two sides of the same coin are really important in building somebody´s personality and relies mostly on the people who surround him/her (parents, family, baby sitters, etc), and depends on the relation he/her has with every person he/she believes important.