The update - which is part of a new policy targeting a controversial sect of influencer marketing - could even see some posts removed entirely.
Instagram will apply the age restriction when posts feature an incentive to buy or include a price for a product.
Meanwhile, the social media platform will delete a post if it "makes a miraculous claim about certain diet or weight loss products, and is linked to a commercial offer such as a discount code".
Although the site's advertising guidelines and policies never actually allowed for these products to be promoted, the company insisted growth amongst influencers and celebrities has prompted them to take further action across both Instagram and Facebook.
In a press release, the brand's public policy manager Emma Collins said: "We want Instagram to be a positive place for everyone that uses it and this policy is part of our ongoing work to reduce the pressure that people can sometimes feel as a result of social media."
And Jameela Jamil - who previously founded the I Weight movement in reaction to such issues on social media - added: "Facebook and Instagram taking a stand to protect the physical and mental health of people online sends an important message out to the world.
"I'm thrilled to have been able to work towards this with them, alongside a host of other experts who shed light on the danger of these products."