It is rather pleasant. Though at first I thought for sure it was a name from another culture - Arabic perhaps. The thought of using the English verb "aim" as a name is very modern and cutting edge. I too like how simple it is, and it does have a nice sound to it.
Boy or girl? I suppose it works well for both - female Aim is similar to
Amy. I immediately thought boy, however. Perhaps because of the inherent underlying "hunting" or "soldier" reference in the word aim... like ready, aim, fire.