Unfortunately, adult children of U.S. citizens can’t adjust status inside the U.S. if they’ve overstayed. You’d likely need to leave and apply from abroad, which could trigger reentry bars.

If you were under 21 and unmarried, it might’ve been easier. But as an overstay and likely over 21, you’ll be in a visa category that doesn’t forgive unlawful presence. It’s possible to apply through consular processing with a waiver, but that process can be tough.

U.S. citizen parents can sponsor adult children, but it gets complicated when there’s an overstay involved. For unmarried sons and daughters over 21, the visa category (F1) doesn’t offer the same protections as immediate relatives. Since you overstayed, adjusting status from inside the U.S. probably isn’t an option unless certain exceptions apply. You might need to apply from Vietnam and file a waiver for unlawful presence. It’s best to speak to an attorney before making any move, they can assess if any exceptions apply to your situation.