Who must be 21 years or older to petition for siblings under F4?

To successfully petition for siblings under the Family Fourth Preference (F4) category, the petitioner must be a U.S. citizen. Specifically, to file for a sibling, the petitioner must be at least 21 years old. This age requirement is in place because it reflects the legal capacity to sponsor someone in this immigration context.

In this case, choosing the U.S. citizen petitioner is the correct choice as it aligns with the regulations set by USCIS regarding family sponsorship. Siblings can only be sponsored by a sibling who has reached the age of 21, thereby ensuring that the petitioner has the legal status of an adult and can take on the responsibilities associated with being a sponsor.

The other options do not meet the criteria. A lawful permanent resident (LPR) cannot petition for siblings, as this privilege is exclusively reserved for U.S. citizens. The sibling applying does not have an age requirement for petitioning, as they are the beneficiaries in this scenario. Lastly, a spouse of either the petitioner or the applicant does not affect the sibling's petition and also does not need to be 21. Thus, the requirement for the petitioner to be of legal age is crucial in this immigration process.