Arhaan Ahmed

I loved the movie , it was absolute wonderful performance by all the actors and actresses, especially Amitabh Bachan, just wondering that why is Rohan Mehra, the son of legend actor Vinod Mehra mentioned in the cast of the movie as he was born on the 8th of April, 1990 and the movie was released during the year of 1979 , so how can he be mentioned in movie where he is not even born in?, is google mistaking Rohan for Vinod Mehra?, as this is so weird?. I think Google has made a mistake