Rationalization time:

^This guy is at least a 1000 years old. He was sent to Middle Earth around year 2000 of the Third Age, and the War of the Ring occurred in year 3019 of that age. Gollum, through the power of the ring, was able to live about 570-600 years. So, it's not impossible when magic is involved to prolong age indefinitely.

Judging by the scenes of Canterlot when Granny Smith visits, the style of dress is approximately that of the First Industrial Revolution (late 18th Century to early 19th Century), which would be a little over two-hundred years ago. Granny Smith could have, for her work or through the magic surrounding the Zap Apples, achieved uncommonly old age.

There still remains the problem of Stinkin' Rich being the the great-grandfather of Diamond Tiara and the grandfather of Filthy Rich – assuming it did occur 200 years ago, that would require them to have given birth to their offspring in their fifties. It's possible through that family's exposure to high amounts of the jam led to slightly prolonged lives, though less so than Granny Smith herself. Plus, judging by the gray tint to Rich's mane, it's possible that he is approximately that old anyway.

So technically 200 years ago would be hundreds, as Twilight said, and Granny Smith could still have founded Ponyville.

When in doubt, bronies, blame it on the magic!

@BulletproofBrony