Tell My Younger Sister?

I mentioned in a past post that the only person in my family who doesn’t know I’m gay is my little sister. Having anybody in my house not know bothers me, but as I was coming out to the others I knew she would be the last to know. My parents would resist telling her, and to be fair she’s separate enough from me in age that I can deal with her not knowing for a while. Still, as a member of my family she has a right to know before everyone else does.

She's only in sixth grade, but she'll be thirteen in September, she’s very smart and independent, and I’m pretty sure she has G-rated knowledge of what the word “gay” means (and if she doesn’t she certainly will soon, whether I’m the one to say it or not). This coming summer she’ll be readying for junior high and I’ll be readying for my last year living at home, while I’ll still have some control over the situation. I’m looking at late June or early July to tell her, because in the summer I'll have the time and space to do it right. Inevitably, of course, Mom and Dad will have something to say about it, but my intention is to get it done.

I have three questions here: “Would I be right in telling her?” (is she old enough, is it too soon?), if so “How do I tell her?” (alone or with my parents present, bluntly or cautiously, that kind of thing) and (this last one may not be necessary, if I can get the communication about this established the way I want to, but just in case I’ll ask) “How do I tell my parents I’m going to tell her?” Any advice would be appreciated.