You can't really tell by the size. I have one snake that was born in 2006 and she's about the same size as one that was born in 2007.
Your snake looks like a yearling. As far as the sex goes, you're going to have to have an experienced breeder, vet, or reptile store person sex them for you, as it can be potentially harmful to your snake to try and do it on your own. There are two proven methods: Popping, and probing. Popping can be done while the snake is still young. However, popping is not 100% foolproof. Probing can be done once the snake is older. Again, it's not 100% foolproof, but it has a better accuracy rate than popping.