Memories

Talking to a friend about memories of our childhoods we realised that different people can remember further back into their past than others and we couldn't figure out what the factor was that helped people remember further and better? So I got thinking, is it how imaginative people are? Or how much they remember stuff as they're growing up, (I was always chatting about the past with my mum when I was younger)? Or something in our brains / genes?
How far back can you all remember and any other ideas of the reasons why?