Welcome! This forum has a treasure trove of great info – Scouters helping Scouters! Just a heads up, though - all content, information, and opinions shared on this forum are those of the author, not the BSA.
Scouts who are >18 remain on the Scoutbook roster to allow time to complete any last awards they may have earned before 18, Mark all awards awarded etc. Since it is very difficult to write an algorithm to figure out which Scouts need to remain, the decision was made to leave all > 18 on the roster. You can remove them by putting an end date on their membership entry.
We are working with BSA IT to fix the < 18. They should have been removed from the Scoutbook roster.
We have two who are greater than 18, in fact one is already 19 and they are still listed in Scoutbook. I went in and added a membership end date. Hopefully that will remove them from our Troop in Scoutbook.
Scouts who are 18 on January 1 remain on the Scoutbook roster to allow the unit time to make sure their records are fully up to date. We are working with BSA IT to get Scouts who are not 18 on January 1 removed from the Scoutbook roster if they are not continuing when the recharter is processed.