Progeria is a genetic disorder which causes premature ageing,but in this case though Amitabhs makeup is good,the question most in my mind is his height over six feet is not suitable for this role how is th director going to justify this,Children suffering from Progeria are generally short and lack proper growth,this is something the director has got to look into,besides its nice to know Amitbh taking pains for this role with great make up,but at the same time the director could have taken a talented 13 year old and done the nessesary makeup to achieve a far realistic role since we all know Amitabh is doing this role,his superstardom and age is going to affect the movies verdict.
What difference does real age makes, as long as they are not playing Shashi Kapoor or Amitab Bachan on screen. They are playing some charecters and if it looks believable on screen there is nothing wrong.