Coconut Battery is an app (
link). It has an indicator for the age of your machine (see attached).
The bottom line is that it is impossible to put 30 charge cycles on a notebook in 4 days of usage. This is a no-questions asked exchange. Set up an appointment at the Apple Store and get it exchanged.
Apple has a 14 day return policy with MacBooks. If you are not satisfied for any reason you can return it for a full refund (if you want). There isn't even a restocking fee, so there should be no reason why you can't get this resolved easily.
The only thing you need to do as an additional step is make sure you are getting the newest model with a new battery.