I'm not an only chid but my daughter is. It is a very different expereince from not having siblings.
Yes, very few people grow up without a sibling, either biological or adopted
I think being an only child can have pros and cons. You get the full attention of your parents, for example. 
I am kind of an only child however, the true defination says someone who has never had a sibling, I have one but we were seperated when we were 6 
Yes, you must definitely feel like an only child. Did you get to reconnect later in life?
we do not really speak, my understanding is that being an only child throughout history is pretty uncommon, except for in china I guess