Wikipedia can sometimes be a questionable source, but it'll do for now. The Oort Cloud description gives us a ballpark figure of at least a light-year for the distance to this hypothetical planet. So if this thing really did exist, and it's got just 7 years to reach the inner solar system, then it's not so much an orbit as a one-shot flyby, and very, very unlikely.

1/7th the speed of light is well into the realms of relativistic velocities, as well, so if these Mayans knew where it was then I'd like to see some other evidence that they knew about the speed of light and Special Relativity.