"Purchase Date not Validated" When checking MacBook Air serial number

An incorrect purchase date cannot be corrected online. You need to contact Apple Support by phone:

Update your proof of purchase

Who/what is flipkart? Never mind, I see it's an online store that sells everything......

Obviously not an authorized reseller.

Is the device supposed to be new? Still in factory sealed box?

If someone bought a lot of older machines, the warranty may no longer be valid or there could be a number of other reasons. If it is new, you would need to contact Apple with proof of purchase receipt to change your warranty details.