One issue we had with a student that wanted to come back to help was that he was very "productive" while a student. When he came back he tended to want to do more than just mentor. (Our team sturcture is the kids do almost all of the fabricating). We had to pull this student aside and teach him what mentoring is/means for our team. A year later things are working much better. He has also learned that he should be involving himself in other college related activities to round out his college experience.
That being said another one of our mentors is a past alumni that came back after college. There was enough seperation there that all of the students were new and she could get the repect of being a mentor instead. Only having seen those examples, I could understand a rule of requiring a new college grad to sit out one year.
On a slight tangent. Many universities do not allow alumni to become professors at the university they got their PHD because of imbreeding identical thought processes. If you take a HS Senior from your team and immediately bring them back, they may be more likely to stick with the same habits as opposed to learning new things.
One suggestion for Freshman that still want to be involved, why not get on a regional (or District in Mi) planning committee. This should help you get a whole new appreciation of FIRST and give you brand new skills.
