According to Youtube policy, a channel must has 4000 Watch Hours & +1000 Subscribers in 365 days to start review for monetization.
It's not easy to get this requirements, many people take more than 1 year still not get enough if only develop channel in normal way ( upload video, share social, watch by themselves ) because this way was old and not effective.
To get 4000 hours and 1000 subscribers and 1000 subscribers to review for monetization, people are tending use Google Adwords to advertise their video. It will be easier to get these one and legal with Youtube policy. Besides that, Youtube is also encouraging people use that to fulfill their requirements for monetization so it’s the reason your channel can be easier to pass the review.
Actually, if don’t know the way to advertise video on Google Adwords you should choose AudienceGain Net as a professor can help you easier to get Youtube's requirements for monetization.
From our experience 5 years in Social Marketing we can confident to helped you shorten time, get 4000 watch hours and 1000 subscribers by Google ADS in the fastest and safest way!