So the id exists at birth, but the other two parts of the personality develop later - how much later? when is personality finished?
For Freud, the three parts of the personality develop in a series of stages. Because he focused heavily on the sex drive, he believed that the stages were determined by the developing sexuality of the child. At each stage, a different erogenous zone, or area of the body that produces pleasurable feelings, becomes important and can become the source of conflicts. Conflicts that are not fully resolved can result in fixation, or getting "stuck" to some degree in a stage of development. The child may grow into an adult but will still carry emotional and psychological "baggage" from the earlier fixated stage.
ORAL STAGE: Weaning and Oral Fixation
The first stage is called the ORAL STAGE because the erogenous zone is the mouth. This stage occurs from the birth of the infant to about 1 or 1 1/2 years and is dominated by the id. The conflict that can arise here, according to Freud, will be over weaning (taking the mother's breast away from the child, who will now drink from a cup). Weaning that occurs too soon or too late can result in too little or too much satisfaction of the child's oral needs, resulting in the activities and personality traits associated with an orally fixated adult personality:overeating, drinking too much, chain smocking, talking too much, nail biting, gum chewing, and a tendency to be either too dependent and optimistic (when the oral needs are overindulged) or too aggressive and pessimistic (when the oral needs are under indulged).