@enbypirate @meadow Cool question with Ig Nobel Prize vibes, "honor achievements that first make people laugh, and then make them think." I like (3) best. A shapeshifter loses control over the forms they can take with time, just similar to mortals who lose mobility, dexterity etc. when they grow older, so they can only shapeshift into older shapes.
Maybe the energy required to shift into forms increases with differences of actual and intended forms. It costs increasingly more to shift into a younger form as the shifter ages.