One reason is amitabh took a break.then made a come back.so his age was evident.But khans worked continuously without any break.So since people are used to seeing them regularly age is not evident that much like bachan.When we see an actor after many years we can identify the differences in looks more.
QUOTE=Lord_Voldemort]
Did you forget his awkward phase where he tried to still pass off as a hero in his 50s romancing actresses in their 20s and got rejected by the audience?


It was when he was so badly rejected as leading hero that he started doing older roles in films with younger heroes.
Unlike him, the Khans are relatively better placed since they are still calling the shots in the industry and we are yet to see a bigger star.
Yes, Shahrukh is going through a low phase, so he might be the first one to start playing older roles.
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