iOS 7 is the mobile OS from a whole new experience. With an all-new design and more, iOS 7 is available on: -iPhone 5, iPhone 4S, iPhone 4 -iPad (4th generation), iPad 2, iPad mini -iPod touch 16GB, 32GB, 64GB(5th generation), iPod touch (4th generation)
iOS 7 will not be on the iPod touch 4g 16GB. This is because iPod 4G is powerful enough for the update. You can buy anther iPod generation if you want the iOS 7. The new 16GB iPod Touch 4G was just released a while ago.