Before this you need a 10k subscribers on your YouTube channel to use the mobile live streaming feature. Live streaming from mobile feature have added in the Feb of this year by the company. The feature works same like Periscope and Instagram's live video feature.
To see if you have the feature enabled, press the floating record button on the Home screen of the YouTube app. You should see a 'Go Live' button in addition to the standard record button. Let us know in the comments if you're seeing it or not.
Google's updated support page with the new terms for using and creating a YouTube live stream. They clearly mentioned that the user need 1000 subscribers to stream from the mobile device.
Keep Your YouTube app updated with the latest version. Go through the below link to download the Latest YouTube Android app.
Source : AndroidPolice