Yep. I did. I started when I was 19, I'm 26 now, and I was kind of nervous because I thought I need more life experience. It was pretty cool. The little brother I had, he was 10, his dad and older brother was killed in a traffic accident and all he had was just his mom and grandparents. He wasn't a bad at all, but he was a little rough around the edges and he was surrounded by bad influences. He turned out very good. He is 17, made the honor roll all four years of his school, he is going to Stanford he wants to major in chemistry and he has been trying to get in shape for track. We talk almost everyday.
My experience has been great, you should try it. Don't be afraid about getting some knucklehead child. You are going to get someone that wants to have someone spending time with them, helping them out, guiding them you know. So try it.