A tenderpaw may not remain so for more than two years. However, the minimum age for the next rank of guardmouse is four years higher that the minimum age for tenderpaw. How do you resolve this conflict for tenderpaw that both must and cannot promote?
The rules state that if a tenderpaw fails to achieve promotion to a guardmouse for two years in a row, they are retired from service - a sort of embarrassing failure that proves that they don't have the right stuff.
If a tenderpaw fails to be recommended for guardmouse rank, he has two options. He may retire from the Guard. Gwendolyn and the other guardmice thank him for his service and return him to his parents. No hard feelings, no harm done. Alternatively, the tenderpaw may choose to do another year of patrol with his mentor. At the end of the year, he will be once again considered for promotion. If he fails to make promotion this second time, he is quietly retired by Gwendolyn and sent home to his family.
However, a tenderpaw can enter into service at age 14, while the minimum age of a guardmouse is 18.
Mice can enter the guard as a tenderpaw as early as age 14. They can be officially inducted into the Guard at age 18. Most guardmice retire before the age of 60.
What happens to a tenderpaw that is age 14 who completes his first year? Do they:
Not check for promotion - their years before age 18 do not count for or against them. They will first be checked for success or failure of promotion on the year that they're 18 (or possibly 17, if their birthday is in the winter?).
Check promotion only for success - if they pass, this promotion will be applied once they are of eligible age, and they will continue as a tenderpaw until then; if they fail to be promoted, it is not really a "failure" and is not counted against them.
Check for promotion fully - if they pass, this promotion will be applied once they are of eligible age, and they will continue as a tenderpaw until then; if they fail, it counts as one of their two strikes.
They just fail after two years - this paradox means they are doomed to failure. (It's probably not this one).
I would probably suspect it's either 2 or 3. In this case, a tenderpaw would be promoted to a sort of "junior grade" guardmouse position, which would mean that they earned their promotion but cannot yet hold the full, official title. They then become the real deal once they reached the requisite age.