You will not only make yourself a new friend, but you will be giving cyberculture a good name as a friendly and fun place to be. Give people the benefit of the doubt, don't assume they know better. Tell them politely, and they WILL know better. True, part of the appeal of the net is the fact that you DON'T have to be yourself, you can be whoever you want to be, with a slim chance of anyone knowing otherwise. However, there is a line between protecting yourself and misleading others.
People form very close friendships on the net, some even get involved in romantic relationships.
It hurts allot when someone finds out the 19 year old girl they were becoming friends with is really a 45 year old man. If you really want to make new friends and get to know other people, don't lie about the basic fact of who you are. They don't need to know your real name or your age or where you live unless you choose to share this info, but you cross the line when you portray yourself as someone you most definitely are not. There is no way to know for sure who you can and can not trust on the net, except to hope that a majority of the chatters are there for the same reasons you are and do not intend to lead you on.