Peer pressure is not something that simply disappears at a certain age. Peer pressure is in our lives and is used by family members, employers, and many others. I believe peer pressure is a common part of life and is not particularly unhealthy. It makes a person question their beliefs and stand up for them, when need be.
Often times, peer pressure makes people want to cave into what people think - and not what you, yourself, believe. It makes you feel like you're the one being weird and different and therefore you feel a need to "go with the flow" or follow other people's opinions and/or ideas. Eventually that will probably make you feel ashamed of yourself for not being who other people "want" you to be and you'll end up changing yourself for other people - even if you don't realize it.
That's not healthy for your living.
I believe that the existence of peer pressure is not healthy. Peer pressure can make a person do something he or she would never do unless pushed by his or her friends. It is very difficult for a young person to resist peer pressure because they want to be accepted by the group.