What makes my memory so good?

I don't have a photographic or eidetic memory but I have an extremely good memory for details and information. I can remember the plots of books I read years ago, and dialogue and scenes from movies. I remember things from as far back as 2 years of age with strong clarity. I can even remember obscure conversation topics I had years ago, dreams I had years ago, and even feelings I've had at certain ages. When I say feelings, I mean my perspectives based on my age. How I felt the time I liked a girl, things that seemed bigger or more challenging when I was younger like giving up the bottle or pacifier etc. I also get aggravated when people repeat things as I have remembered what they said. Don't get me wrong; I forget things like everybody else but I was curious as to why my recall is so good. My IQ is only slightly above average and I suck at math. My brother probably has an way above average IQ; he can do physics and fix electronics but his memory is awful. He even says "I don't remember what I had for breakfast today." What is different about our brains? Do I have more neurons? Are certain parts of my brain thicker or bigger?