This is simply a metaphor because it is comparing one thing to something that is very much unlike it.
B is correct, "<span> Christina and I went to the same summer camp for years (since we were 8)" </span>parentheses are used when you have some extra information you want to add, but its not completely necessary. Like how they started going to the same summer camp when they were 8, you can still read the sentence fine without it, but it's a nice piece of information.
