The USCIS has not updated their sites and information, but there indeed was a BIA ruling years ago. The K-2 does not 'age-out'. File for the K-2 AOS at the same time as the K-1. No I-130 needed. Include a copy of the Matter of Le BIA ruling and point out that the K-2 is still eligible to AOS, even though they turned 21. This may help if whatever adjudicator happens to receive your case is not aware of the old ruling that USCIS is not updating about.
The BIA ruling in 2011, Matter of Le > http://www.legalactioncenter.org/sites/default/files/docs/lac/Matter-of-Le-Decision-6-23-2011.pdf
As long as a K-2 entered the US before turning 21 and the K-1 parent married the I-129F petitioner within 90 days of entry, then they are eligible for AOS and do not age out.
A K-2 does not need to be under 18 when the K-1 parent's marriage takes place. The K-2 just has to receive the K-2 visa and enter the US with it before turning 21, and the K-1 parent must marry within 90 days of enter with their K-1. That is all it takes for a K-2 to be eligible to adjust status.
USCIS Q&A from 2012. The USCIS is slow in providing updated info and guidance on new laws/rulings, but at least it was mentioned here > http://www.uscis.gov/sites/default/files/USCIS/Outreach/Notes%20from%20Previous%20Engagements/2012/October%202012/AILA-Liaison-Committee-meetingQA.pdf
You can find several articles and lawyer sites discussing the ruling if you Google something like "K-2 age out'.
And this is from 2015 and proves that USCIS is slower than a weighted down turtle traveling through a molasses ridden tar pit. They have drafted the guidance, but the internal review is lasting for years. What a load of lazy BS >
https://www.uscis.gov/sites/default/files/USCIS/Outreach/Notes%20from%20Previous%20Engagements/PED-Field_Ops_Agenda_October_2015_Cleared.pdf
K-1 Matter of Sesay and Matter of Le Guidance 7) During our liaison meeting on March 21, 2012, USCIS stated that it had drafted guidance related to Matter of Sesay, 25 I&N Dec. 431 (BIA 2011) and Matter of Le, 25 I&N Dec. 541 (BIA 2011) and that the guidance would be issued soon after the completion of an internal review.8 Please provide an update on the status this guidance.
USCIS Response: USCIS has draft guidance related to Matter of Le and Matter of Sesay. This guidance is currently undergoing internal review.
