A free app for Android, by Kim Mik.

Old To Young Photo Editor is a photo editing app that allows you to change the appearance of your photos.

Just take a picture of yourself or anyone else, and apply one or more of the various face changer stickers that are available. 

You can rotate, resize, or move the face changer stickers around your photo until you are satisfied with the results.

If you want to know how you would look as a younger person, just install this photo editing app and see for yourself.