Ganny smith's age

Fair warning this is just a head cannon of mine.

I've seen a lot of the reviews of MLP, like Silver-Quill, talk about how Granny smith's age is a continuity issue. How I do see it as a problem, there has always been this little head cannon of mine that dismissed this issue as well as how the princesses have lived for so long. Yes I know a lot of people just view the princesses as immortal beings, but honestly I don't really like that idea. If the princesses were immortal it would make me have more questions then answers like "If they are immortal then why have a royal guard?" Being immortal means death is not possible whether by age, sickness, or injury. So what the point of a royal guard? They would be pointless granted they are pretty useless already in the show. Anyways back to my head cannon, what if instead of the princesses being immortal, and to fix the whole age thing with granny, that age is decided by how much magic a pony has.

Let me explain, in the two part episode Twilight's Kingdom with Tyrek we learn that earth ponies, pegasi ( <-- I cant figure out how to spell it sorry), and unicorns have magic. So since each pony has magic it would make since to me that each one has a different level. Unicorns would have the greatest amount after Alicorns, then pegasi, and finally earth ponies. Though there is different levels between the races there is a certain average amount of magic leading to an average life span. Though because Alicorns have the most amount of magic they age slower thus a longer life span, but can still perish from illness or injury. Granny smith is an earth pony yes, but she has a great amount of magic that is slowly aging her. We know granny smith is strong granted not as strong as a younger pony, but still strong enough to help Applejack on the farm as well as jump in a circle over water cans to make zap apple jam.

Like I said this is a head cannon and you will see this again in my friendship of a dragon story. Have a nice day or night! ^^