The average data a person uses per month varies as to whether they use the data on their mobile devices or on their home internet.
For mobile devices the average user of a mobile device such as a smartphone uses on average 2 GB to 5 GB of data per month.
But for home internet uses on the low end people use around 50 GB of data per month and some use as high as 200 GB of data per month if they stream a lot of movies through Netflix or watch a lot of youtube or download a lot of stuff.