I think you need to have a star to be a Sage. Sages have 170+ (like me--hooray), but also have that track record of posting serviceable information here.
I'm not actually sure what the requirements are to be a sage, but you do indeed receive a star when site staff have observed you to be a very helpful, active, and insightful member on the forums over a period of time.
@"Theo - 7Sage" What is the process of becoming a tutor on 7Sage? Is a Star member just a full time member? What is the approval process like? Does one just need to submit one's official test score screenshot? Thanks!