Self-esteem is not a constant thing.  It can increase or decrease as people continue to interact with their family, their peers, and their community.  On average, your self-esteem drops swiftly down in early adolescence, increases gradually during adulthood, and decreases gradually again towards the end of your life.

Childhood:  Young children need constant support and encouragement from their family members in order to keep their self-esteem level high during adolescence.  If they have the chance to succeed at small tasks and goals and to build their skills, they are most likely to grow up to become very confident and successful individuals.  Most children enter school with a relatively high self-esteem, but there is often a gradual decline in self-esteem during their years during elementary school.  This may be happening because students begin to compare themselves with other children.  Or the students may begin to receive more negative feedback from teachers, peers, or even their own parents than they had ever received before.

Adolescence:  It is very normal for teens and adolescence to be critical of their outward appearance, their abilities, their interests, and their own shortcomings.  But some teens (there are always a couple of these present in every community) are overly self-conscious and often tend to judge themselves way too harshly.  They may end up comparing themselves with only the best atheletes or the most attractive celebrities.  As a result, their already wek/low self-esteem may suffer significantly and even drive them to depression or withdrawal from society.

The larger world around you constantly has an influence on your self-esteem.  You receive messages about your appearance, your gender, your cultural group, and your values from the ever present media.  Messages like "only thin people have fun" or "only the latest electronic gadget will make you popular" can surely make you feel that you are not as good as the others who have these traits or things.

Adulthood: Self-esteem generally rises during adulthood and peaks at the ages 60-69.  Adults  at this age begin to accomplish their bigger long-term goals and take complete control of their lives.  Also, adults are better able to keeping the right things in the proper perspective.  Researchers are not sure why adults' self-esteem tends to decrease in older adults, the elderly.  The drop most likely is caused by many the health problems that plague the lives of the elderly and also because of limited roles for the older adults in our society.