I updated the Play Store and YouTube is not working on Galaxy A5.
If the application is not working anymore, go to Settings > Applications > All tab > Scroll down to YouTube and tap on it. Tap on Clear data and Clear cache then start the app again and it should work. If you still have issues, delete the application from your computer and reinstall it again.
Download page: https://play.google.com/store/apps/details?id=com.google.android.youtube