There are a lot of aspects to be discussed, when a Super Star acts in a movie despite his age.
One aspect out of dozen is
This movie has two supporting character Shiva-Rajkumar and Mohanlal. For common audience these character are nothing but to assist the goal of our hero.
Actually NO. Why?
These two characters even though they represent outside the body of Rajini actually they are Rajini’s extended version.
See when Rajinikant was young he did all these character together in Basha. But today matured audience will not accept those character of Rajini considering his age put together. Hence the Director was smart, he took some of the character from Rajini and made two supporting character of Rajkumar and Mohanlal for just for the common audience logic.
In Real, The Raj kumar and Mohanlal are to be seen as a part of Rajini with additional two bodies(or avatar).
Superb Movie!