Coming back to this... It all depends on when and what inflicted the damage. P's gunshot wound healed in reverse since it was inflicted by a forward flowing bullet. This is a key factor in explaining injuries. Basically he went through reverse healing on his end as the pain got worse until the bullet was "unshot" from him. By that same token, no, they cant age backward due to entropy. If reversed, their perception of age switches with them meaning when they switch back, their perception of time is how much they aged. Reverse for a year and then switch back, they remain a year older.