I was an only child, which used to be very uncommon.
Yes I do think it is very uncommon. My mother is an only child and she really felt the effects of it when her mother became to elderly to care for herself, and my mom has no siblings to help
I wish I would have had a sibling to grow up with me. I missed that strong emotional bond.
Yes theres that too. I wish I could say I understand but I don't, I have a little brother.
I would imagine your relationship with your brother is a very unique one.  Like a friend with the closeness of a parent.
When we were younger we would fight alot. We would try to beat eachother up and get really mad when we would make fun of eachother. Now that were grown and he lives so far away we get along much better. 
I would imagine that as children, it would be difficult at times.  I did have a half-sister when I got older, but she lived apart.
Yes but mostly rewarding. Who would you have to do crazy stuff with when your parents leave you at home without an adult? That was always fun. We would get in plastic tupperware bins and slide down the stairs inside of them! Lol