Charles, you do that anyway. Unless there is a special circumstance that would cause you to graft juvenile wood to rootstock, all grafts use mature wood capable of fruiting. The additional years after grafting are to allow the tree to grow and gain the resources to maintain fruit. In the couple years after the graft, the tree may flower and possibly fruit. but since the tree is young and not well established, the fruit is of lower quality. At least that is how I have understood it.
Barbara