What age to allow your kids on social media?

I was thinking today about how my 13 yr old nieces still are not on social media and I give my brothers a lot of credit. I think it’s hard enough going through middle school with all the gossip. I feel like I’m middle school it could just be another source of instant judgment and ridicule. I don’t see how children younger than 16 could benefit from social media. The only way is if they are volunteering their time for the sake of others. For instance, my one niece has a website where she raises donations through baking cakes. She advertises her services through the website.

What is everyone else’s opinion?