I would add more plants first, I love the looks of a planted tank and it will feel great to have a good looking tank once it fills in. See the planted forum for more info on that. They're very helpful
I would also change the background. It's just got too much going on and it makes things look funny IMO. I would just stick with a flat back background and add some driftwood to the right side if you can.
I would also maybe move the bigger rocks around and make the wood a focal point. Maybe get some mosses or java fern to plant on them and make it look more full. Those are just things off the top of my head but for a 12 year old it looks fantastic!!
Just add a little bit here and there and it will look even better!