Youth – Milk Consumption Decreases (11-12 years)

I am making the following statement in a paper but am having a hard time locating a source to validate this as fact. Can you please help?

“It is not surprising that milk consumption dramatically declines for youths at 11 and 12 years old. It is precisely at this age when youth start seeking less approval from parents and adults in their lives and begin to seek acceptance by peers.”