"Age Doesn't Mater in Bollywood," but I think the quote above, from the bit on SRK in KKHH, says it all. If we like actors, we're much more ready to take them in any role, no matter how absurd. Not completely ready, of course, as every now and then we are collectively repulsed. It would be an interesting study to see how this phenomenon plays out in various cinemas around the world. I'm sure Hollywood does it all the time but I'm having trouble thinking of an example - the things that leap to mind are notable because of the age difference between the male and female leads, not necessarily because of the age of the actor compared to that of his character. I know it's common in tv, when 20somethings regularly play high school studens.
Main Hoon Na of course plays it just right - we get our beloved SRK in the golden plot mine of college, but there's no pretending he's 22. Instead we pretend he's 30, but that's a little easier to swallow with my Lays and Pepsi.
I also have to stick up for my man and wonder why Akshaye, who was born in 1975, is flagged twice for age violation, whereas Salman, ten years his senior, is panned only once - and that for a film made two years before the ridiculous pairing in Lucky. They seem to have it out for his hair - there's no mention of him otherwise looking too old or not being able to act the right age. All of the leads of DCH were far more believable as recent graduates than Salman or SRK.
Aside to costume designers: certain actors would look much less silly as college students if you didn't put them in such insane clothing. Not all college students wear pleather to class, you know.