Twitter and Facebook have also set 13 as the minimum age users can join their social networks, so in a sense Google is simply following their lead.
While most teens worldwide can join at 13, Google set the minimum age for new members at 14 in Spain and South Korea, and 16 in the Netherlands.
"Teens and young adults are the most active Internet users on the planet," explained Bradley Horowitz, Google's vice president of product management for Google+. "And surprise, surprise: They're also human beings who enjoy spending time with friends and family. Put these two things together, and it's clear that teens will increasingly connect online."
Google is taking care to make sure teens share what they want to share in the right context, a bid to staunch the gross oversharing on social networks between teen connections who may be more acquaintances than actual friends.
To wit, when teens go to share outside the Circles they've created, Google+ will encourage them to think before they post.
To encourage safe information sharing among teens, Google has made it so that only those teens' Circles can contact each other via chat sessions.
There are other areas where the discretionary sharing controls are more dicey. For example, if a stranger outside a teen's Circle joins an ongoing Hangout video chat session, Google+ temporarily removes the teen while the stranger is active in the session.
Google also announced several new Google+ Pages teens might be interested in, including 106 and Park, Ashley Tisdale, Big Time Rushm Cody Simpson, Teen Vogue and Glee.
Google's welcoming of teens to its social network came two days after the company announced it will support nicknames and some vetted pseudonyms.