Our galaxy itself seems to be rather old, maybe 13.2 billion years old, but the thin disk itself seems to be much younger.
This seems to indicate that the age and shape of the galaxy has changed over time and so it's likely that the rate of rotation has also changed over time. For example, some estimates I've seen show that the thin disk, where we are, may only be 7-10 billion years old. If that's true then the area where Earth is located my only have made about 30 trips around.
Anyone so limited that they can only spell a word one way is severely handicapped!