As the old adage goes - Actors don't have a shelf life but actresses 30+ do. To substantiate this further, one can take the example of Amitabh Bachhan who still reigns at 60+ but a Bipasha Basu is considered to be "looking older" when paired against Neil Nitin Mukesh!

24-year-old Katrina Kaif gave a cold sweat to Aishwarya Rai by replacing her thrice - as the actress with most Internet downloads, ambassador of a jewellery brand and now as the Indian face of Barbie. She has also replaced 33-year-old Sushmita Sen for an endorsement deal with shampoo brand Pantene. 

It is a natural phenomenon that actors have a very short span of life as most of them start early and by the time they cross 30, the nature of the roles they get are more mature than candyfloss stuff. So the industry is always on the lookout for young blood.

Other young actresses like Deepika Padukone, Kareena Kapoor, Priyanka Chopra, Sonam Kapoor and Genelia D'Souza too are walking away with the lion's share of films and brand endorsements in the industry these days. Deepika has been cast instead of 35-year-old Aishwarya in Kalpana Lajmi's "Singhasan". She has also bagged the Bharat Sanchar Nigam Ltd (BSNL) ad from 34-year-old dimpled beauty Preity Zinta.

Bollywood's size-zero queen Kareena, 28, nudged Aishwarya out of the Filmfare Top-10 Power list. And 'Masakali' girl Sonam Kapoor has succeeded Aishwarya as the Indian face of cosmetic brand L'Oreal.

After the success of "Jaane Tu...Ya Jaane Na", Genelia D'Souza has become a sought after name and replaced Preity and Rani Mukerji as the brand ambassador of Cadbury's Perk and Fanta respectively.

Going by the usual trend, when Rekha and Hema Malini turned older, Madhuri Dixit and Sridevi replaced them. When the latter two became slightly older, Aishwarya Rai and Rani Mukerji took their place and now these two are being replaced by Katrina and Priyanka. It's a cycle.

Apart from Tabu, Preity and Sushmita, a lot of the older actresses - Bipasha Basu, Aishwarya, Rani, Lara Dutta, Kajol and Shilpa Shetty - are making few appearances on screen. While some say that they have made a personal choice to do just a few roles in a year, others like Shilpa and Preity are shifting gears between acting and business after they chose to be part of the cricket extravaganza, the Indian Premier League (IPL).

Preity, who recently featured in offbeat films like "The Last Lear" and Deepa Mehta's "Heaven On Earth", says she might get back to her bubbly, girl-next-door image, only if she gets a role with substance.

Tabu, 38, who has been absent from the silver screen after "The Namesake" and "Cheeni Kum", too has only one film "Banda Yeh Bindaas Hai". Similarly, Rani also has just one project in hand - Yash Raj Films' tentatively titled"Hadippa".

And 34-year-old Kajol, who drifted away from the scene after marriage, is doing only Karan Johar's much-hyped film "My Name Is Khan".