Since they both grew up on the Island, I'd say they probably grew up together... Going to School and stuff. I think Abby, Nikki, Shane and Jimmy knew each other pretty well. Maybe Jimmy and Shane were a couple of years older... They would have still spent a lot of time together during High School. That's what I like to think anyway. :)
I know how in episode 12, when henry and sully were about going to shoot Jimmy, Abby noted that Henry had known Jimmy "his whole life", and sagte she had also known Henry "her whole life" (quoted from episode 13), so they probably all grew up together, because they're the same age. I liked how Henry, Abby, Jimmy, Nikki, Shane, and JD all knew each other as kids. I thought it was cool.
