As a green card holder, you can file Form I-130 for your unmarried adult son under the F2B visa category. This category has annual limits, so wait times can be several years depending on demand and country caps.

Currently, the F2B visa for most countries, including Mongolia, can take anywhere from 5 to 7 years or more. You can track progress on the Department of State’s Visa Bulletin, which updates monthly.

Once you become a U.S. citizen, your petition would be upgraded to the F1 category, which may or may not speed up the process depending on visa availability. However, your son must remain unmarried to qualify in either category.