Microsoft rolled out an app for Windows Phone in May called How-Old to demonstrate its new face detection API. The app allowed users to upload images, and then predicted their age and gender. Barely ten days after its debut, it looks like the app is not available for download anymore.
At this stage, there's no indication as to why the app isn't available, but the fact that it is still listed suggests that it could return shortly. Seeing as how the original app was published by Microsoft's Chinese arm (with sharing options limited to Chinese social networks), it could just be that Redmond is working on adding more social sharing features before re-launching the app.
Either way, we'll let you know once we know more.
Thanks Muhd Izzuddin for the tip!