I actually think that site is so unique, it's simple but such a clever idea!
There are a few other age guessing sites out there however Guess My Age was the second one in existence (that I know of) when I set mine up. The owner of the first one got all snotty claiming I just stole his idea which wasn't the case.
Guess My Age is the only website to currently offer this service. There is another website who sell their script, but it's a load of rubbish and not worth $1 IMO. I am also happy to offer better custom branded pages with URLs/background images, etc, for larger websites either for free or as a paid solution. It is also possible to use the website as a feature on yours with only photos you've submitted, for instance, if you own a radio station you could get yourself and all of your DJS to sign up and the photos would only be displayed on a custom page for your station, rather than everyone on there's photo being shown. This would be a paid solution as it's more time consuming to keep it advert free.