Only US citizens may sponsor their parents for Permanent Residency. The US citizen son or daughter must be at least 21 years old at the time they sponsor their parent for Permanent Residency.
Parents of US citizens are immediate relatives, meaning there is no wait time (aside from normal processing times) to be able to request residency for the foreign national parent, once the U.S. citizen child is 21 years or older. However, it is important to keep in mind that being able to sponsor the parent for residency, and the parent being “admissible” to the United States for residency are two different components of the sponsorship process. There are many factors that come into play, especially the parent’s immigration history, especially any entry or visa violations, their criminal history, and their manner of last entry into the United States.
If you are interested in sponsoring your parent for residency, you should consult with an experienced family immigration attorney who can perform a thorough screening of your immigrant parent’s immigration history to ensure a proper filing.