For me, they didn't fully develop until after I stopped going to church. Previously, everything I did was pretty much reflective of an egoist. I wanted to be a good person so that I could make it to heaven. Because of some loop-holes in the religion I felt that I could be a pretty scummy person and still come out on top. That left me in the best of two worlds, I could pretty much do what I wanted, and still get my way in the end. It was a lame way to live.
In the years since my confirmation, graduation, college and countless friendships that have come and gone, I see the world through different eyes. I now live by some sort of a golden rule/utilitarianist/egoist mix. I'm probably some sort of an ethical mutt, but it works for me. I try to do what is best for everybody, but obviously I look out for my own interests. I've also learned that what may be good for somebody else, may affect me, and only benefit that one person out of their own greed. In cases like that, I have no problem looking out for myself.
I also view myself having egoist ethics still, because doing good things makes me feel good, and I like that feeling. So while my current ethical system is guided situation to situation, I feel that it works out and I am a better person for it.