It took me awhile to understand what this site was trying to accomplish. I wonder if it wouldn't make more sense to include a sample definition near the top of the page (under the logo) that describes the process. Show the definition for cat and then what age it is for. Also, since age plays such a big part (at least in your description) maybe you should make that a major part of the selection process.
In the Latest Definitions area I think the posted by is taking up way too much room (in fact it doesn't need to be on there at all). And the definition should be just left of the word taking up two columns. I would also show more than just three.
The header is a little tall for the information there and the login button is way too big.
In the logo I would play up the .az part more than the pedia since wikipedia already has such a brand name. The unique part and the part you want them to remember is the .az.
On the menu, there is too much space to the left of Home.
As for the search, I would make this more prominent...maybe even in the header next to the logo.
The blue boxes below the latest definitions are too bold and non-important in the grand scheme. It isn't about the reviewer or creator but more about the content.
use more color. Yellow and orange goes well with blue.
nicely done !