Well not that I have coined the idea but its concept was already working in my mind until someone spelled it out. This style of mentoring is called 'Reverse Mentoring' which is actually a book written by Earl Creps. He has a website too which you can go to here. I haven't read the book but I think it would be a good read, namely because the title really gets to me (in a good way). He also has an excerpt form the book introduction on his website here.
I'll leave you with this quote that I like from the excerpt:
Reverse mentoring assumes a completely opposite perspective on learning. While acknowledging the proven value of the older-to-younger approach (teaching down), it provides the vital complement of a younger-to-older method (teaching up). Reversing the traditional dynamics feels unnatural to some, especially older leaders like the Baby Boomers who now make up almost half of the American workforce and 60 percent of senior pastors and who have been waiting most of a lifetime to take charge. However, the rate of change in our culture puts younger people in touch with things for which their elders sometimes lack even the vocabulary, suggesting the need to go beyond intergenerational tolerance to reconciliation that leads to a new collaboration.
The young teaching the old represents only an example of reverse mentoring. The key to the relationship is not who is greater or lesser, but the unlikeliness of the learning connection. The reversal is as much one of expectations as of position or age. Every culture subsists in part by having boundaries that define it, but these boundaries also serve as barriers that cut people off from each other, making a teaching relationship unlikely. Reverse mentoring (RM) is cross-cultural in that it actually uses the unlikely possibility of a relationship to benefit both parties through mutual learning through honesty and humility.