If you are a Youtube publisher with an ownership of a channel which is getting much view which make eligibility for you to add Google Adsense to your Youtube Channel then why should you wait.
Here is a simple tutorial which will guide you through all the processes of attaching adsense to your youtube channel:
Go to your channel by visiting Youtube and make sure that monetization is enabled on your channel then follow the below steps.
Move your cursor to top-right side near to your channel Picture next to upload as shown in below picture and click on "Creator Studio".
Now click on Monetization under the "CHANNEL" button.
Now in the same window "Guidelines and information" will be opened under it click on "How will I be paid"
Under the "how will I be paid"Click on associate an adsense account or click here : Adsense youtube
which will take you to this page below in the shown picture.
Now Follow all the steps to add adsense to your channel. Happy Earning!!!