An Eagle Scout board of review may occur, without special approval, up to 24 months after a Scout’s 18th birthday.
See “Boards of Review Must be Granted When Requirements are Met,” 8.0.0.2.
To hold a board beyond 24 months after the 18th birthday, the candidate, the candidate’s parent or guardian, the unit leader, or a unit committee member must submit a Belated Rank Application (11.3.0.0). See item #3 below.
For more detailed information, see See Guide to Advancement Section 8.0.3.1 1.
Guide to Advancement can be found here: https://filestore.scouting.org/filestore/pdf/33088.pdf