I am wondering if you know if there is an age requirement for students to use blogger since I am a middle school teacher?
There is no age requirement on the Blogger end of things. I don't know if your administration/district has an age requirement.
In the 'settings' tab on Blogger's dashboard, you can set up firewalls to keep search engines from finding a blog and to keep anyone from viewing the blog except whomever you choose. These safety features are easy to use and provide a level of security equal to or better than anything a school's IT department could produce themselves.
And it's free.