Aamir wants some more time for Dhoom 3, sending Katrina's and film's schedule for a toss. In the meantime, Kaif is likely to take on the challenge of playing a 62 year-old in Mehrunissa

There might have been much talk about Vidya Balan, undoubtedly the current top actress, having signed the ambitious Nikhil Advani-produced film Mehrunissa, which will star Amitabh Bachchan and Rishi Kapoor, but the producer is currently rushing to London to convince Katrina Kaif for the title role.

And Advani has Aamir Khan to thank for it.

The March-April schedule of the much talked-about Dhoom 3, which will star Aamir Khan as the villain, has been postponed because Khan has told the producers that he is not "mentally prepared" to take on the role yet.

While the recent announcement that the release of Khan's next film, Talaash, has been postponed, has not inconvenienced the rest of the cast and crew, the postponement of Dhoom 3 has affected Kaif's schedule for the year.

Currently, she has three Yashraj Films in her kitty -- Kabir Khan's Ek Tha Tiger, Yash Chopra's untitled film and Vijay Krishna Acharya's Dhoom 3. Now with the delay in Dhoom 3, Advani has taken the opportunity to fly to London to the sets of Chopra's film, to narrate Mehrunissa's script to the actress.

According to a source, Kaif is keen on signing the film but has a few reservations. He said, "Katrina was apprehensive about looking old (age 62).

She also felt she'd have hardly any scenes with the two icons (Amitabh Bachchan and Rishi Kapoor), and that most of her scenes would be with the younger actors who would play the younger avatars of Bachchan and Rishi Kapoor.

However, Nikhil feels she can pull it off." In the film, Kaif will have to play Mehrunissa in two different time periods -- at the age of 20 and again at the age of 62.

The source revealed that Kaif will now join Khan only in April to shoot for Dhoom 3, despite efforts being made to get the actress to shoot her solo scenes for Dhoom 3 earlier.

When contacted, a Yashraj Films spokesperson confirmed that the schedule of Dhoom 3 has been postponed by a month.