How do you know when you are ready?

My wife and I are 20 years old, but we act a lot older (in most cases) then our other, still-single 20 year old friends. While they like to go out and "enjoy" life, we like to spend time with each other and, in many cases, just sit in each others arms while watching TV. I don't think that we are ready of a "little bundle of joy," but it got me to thinking, how will I know when we are ready? I don't know what it is about our lives that makes me think that we aren't ready, so I don't know what it will be when we are.