Age Difference

Just wondering what kind of age difference people had between themselves and the child they adopted. I've been looking at my local online photolisting and was amazed with some of the older children on there, but I'm only 23. I've already e-mailed to ask about what restrictions they have, if any. Most of the children we have interest in are only maybe 11 years younger than I am. I'm ready for the challenge, but what was everyone elses experiences? Has anyone adopted or even fostered a child only 7 years younger? I'm also running into the problem of my siblings ages. My sister is only 17 and my brother-in-law is 18. Do you think it would be an issue adopting a child too close to their ages? any feedback is welcome!