Highly qualified foreign nationals who wait in US for almost a decade to get their employment based green card are not able to file green card for their aged parents. Currently only citizen can sponsor their parents.
Permanent residents should be able to file Green Card for parents older than 50 years. It is really difficult for old parents to wait for their green card holding children to become citizen in 5 years and in several cases more than 5 years before their children can sponsor them for green card.
Many countries treats permanent residents and citizens equal in this regard so USA should also consider providing an option where parents can be sponsored by green card holding children.