Adsense no longer serve ads on YPP videos until the channel reaches 10k lifetime views. This new threshold gives them enough information to determine the validity of a channel. It also allows them to confirm if a channel is following their community guidelines and advertiser policies. By keeping the threshold to 10k views, Adsense also ensure that there will be minimal impact on our aspiring creators.
For some publishers the activation process can be as quick as a day, and for others it can take several weeks. Note that some parts of the process require actions on your end, and adsense can only activate your account after you complete them.