I've had a 2 inch bald spot for over 6 years now & the bald spot has never filled in. Is it too late to regrow natural hair?

If you had a bald spot for over 6 years, it probably will remain bald for life.  You can try Rogaine as you don't need a doctor's prescription to try it.  However it is unlikely it will give you a significant change.

See a very experienced hair surgeon to determine whether this is alopecia areata or some other reason for the baldness. Ultimately you may need this surgically excised or have hair transplants.    

Male pattern baldness occurs gradually over time.  The first sign you may notice will be thinning of the hair follicles into smaller sized hairs.  We call this process miniaturization.  As miniaturization progresses, hair loss occurs and follicles become inactive.  Very often a bald area on the scalp can have a lot of miniaturized hairs even though they are not apparent by the naked eye.  As long as some hairs are present then there is hope to slow or reverse some of the process by a combination of medication and/or cellular therapy such as PRP.  Once the follicles become completely inactive however, hair transplant becomes the best option.  Remember that male pattern baldness is usually accompanied by recession in the temporal areas as well.  If you have not lost hair there, you may have another medical condition for your hair loss.  It's important that you see a doctor specializing in hair right away because the sooner you have treatment the better your chances are for maintaining your hair. 

There is a difference between a bald spot that has been there for 6 years and genetic balding which reflects balding in a pattern or some sort (see web reference below), Bald spots may reflect diseases like alopecia areata (an autoimmune disease) or some infectious cause. You need to see a doctor who understands diseases of the scalp to examine you and make a diagnosis as this is the first step in your process to cure it.