It does not matter at what point of the life cycle you have reached, peer pressure will always be there. Whether your acquaintances or friends coerce you into doing something minor or something illegal, it is defined as peer pressure and it is always the same. A friend will introduce an action to you that may not be what you honestly want to do, but when the rest of the group stands behind your friend, you feel as though you are forced to conform to the behavior, no matter what it is. Each friend after the first that tells you to do it is just reinforcing the action and if enough reinforce it to you, then you will be more likely to conform rather than fall out of line with your friendships. It is one aspect of society I am not proud of.
Peer pressure feeds off of peoples' fear of losing friends due to not conforming to the behavior presented. There are very few, however, who can coerce someone with peer pressure without others backing him up reinforcing it, but then again, there are some people who are able to pressure you more this way. That person will do this by slowly bringing you towards him/her and then everytime they see you, reinforcing the idea in conversation. This will start to make you think about the action more often, especially everytime you see something associated with the conversation with that exact person. There are others that also use the guilt trick to push you into something that you may or may not be comfortable with, and therefore feel as though you need to conform for the presentor, but these cases are extremely rare.
The popular misconception is that peer pressure only happens with high school age children, but in actuality, it starts at the early ages of elementary school and do not end until you retire to the country. People are always going to try to manipulate your thinking and what your beliefs are to conform to theirs. It is a part of human nature to want to feel in charge and to get others to support them. However, you do not have to conform. There is never anybody telling you that you have to do anything: you are in charge of yourself. Only do something if you want to or if you feel it is correct, not because someone else decided to push you into it. Peer pressure is just another one of the many major flaws of society and yet another one that will probably never be fixed.