From what you have said, it sounds like that experience might be too far back. I know MIT has been flexible on that 3 year limit, but only when the experience either has continued more recently (e.g. a team that was formed 4 years ago but continued to work together until 2 years ago) or experiences that had direct impacts on the applicant's work or life today. If the experience you describe happened in your last year of graduate school, it sounds initially like it does not meet those exceptions.

If, on the other hand, that team experience taught you lessons about teamwork and leadership that you continue to apply today in a very direct and relevant way, where it is clear that the lessons make that experience relevant even now, you may be able to write about it. I would call the admissions office and ask. But again, it won't be enough to say "I learned important lessons about leading a team" - you will want to demonstrate specific lessons from that time and how they are directly relevant to your work or management experience today. If you can do that and the admissions office says it's ok to use that example, make sure you focus more in your essay on the current lessons and how that experience is relevant now than on the experience itself.

I hope that helps.