Step 1: An Elderly Woman, perhaps the participant in an experiment?
Step 2:The Elderly woman becomes middle aged, her spine and legs unbend as her bones strengthen and tendons tighten. Muscle returns to the bone, but is till untoned. There is still thickening around the waist as is common. Breasts become slightly fuller, slightly less flacid.
Step 3: Her youth regained! Muscle becomes more firm, breast fuller and more rounded (and in the proper place). Skin becomes taunt and smooth.
Step 4: But something is wrong, the change continues unbidden. The Grown woman becomes a young teenager, still developed, but less fully. Her features become less defined, there is less fat on the whole body as she begins to lose her womanly shape.
Step 5: She reaches pre-pubescence. She is lithe and straight, with almost no curves. She looses her body hair. Her ears and nose are significantly smaller. Her eyes begin to look larger as her cranium becomes smaller.
Step 6: For the second time in her life she is a toddle. Her body tends towards fat, her skin is smooth and hairless. Again her ears and nose are much smaller, and her eyes seem much larger.
Step 7: The regression is complete. She is returned to her infancy.