If i were to buy over a 6-7 month old macbook pro and its original 1 year warranty only expires next June 2016, can I as a second owner of this MBP buy and extend the Apple care for next 2 or 3 years more from June 2016?
I'm not sure if the first owner had registered any Apple care and i don't have his/her invoice when he/she first bought this item.
MacBook Pro with Retina display
Yes. I believe the agreement is for the machine, not the person. It's all about extending the date of the warranty, which you say does not expire until 2016. Ideally, go to your local Apple store with such proof of ownership as you have.
Applecare is tied to the serial number and will extend the regular warranty by 2 years for a total of 3 years (in the US; European laws may apply or differ).
You can easily check the status of the machine by entering its serial number here - it will tell you the warranty status (click on the service coverage system); I have done that before buying a used machine just to make sure.
About your support coverage and service options - Apple Support
Apple Care
