Why do actresses hide their age in Bollywood?

There seems to be this myth in Bollywood that all the actresses need to be younger to sustain and have a long career and that makes them desperately either hide their age or worse lie about their age. Be it, Katrina Kaif, to now even Sara Ali Khan age seems to be a question no one can answer? As Sara Ali Khan, she claims that she's 25, but some sources say she's 27 because she was born in the same year as Alia Bhatt. Plus Katrina is also known to be hiding her age which even made Deepika ask her about her passport on KWK. It is common that actresses have to hide their age if they want to increase their lifespan to work in films. But I guess with Sara Ali Khan joined Bollywood as late as she was at Columbia, because of that she delayed her debut and so she has to hide her age so she isn't competing with the Alia Bhatt, Shraddha Kapoor league and is compared with the younger Ananya Pandey Jahnvi Kapoor lot. What do you guys think about this?