For those who don't know, you can not age kits by size since that varies
and is mostly food dependent at young ages.
 
Here is how you age kits:
 
Average Dental eruption ages (L = Lower, U = Upper for this chart,
C canines which are the conical teeth, P = premolars which are the teeth
between molars and canines, M = molars which are the more flattened teeth
at the back of the mouth, number start toward the front for each type, 49
days = 7 weeks = , 56 days = 8 weeks, 63 days = 9 weeks, 70 days = 10
weeks, 77 days = 11 weeks; you can do the approximate month ages.)
 
Day     Week            Teeth
 
50      7               UC, LC, LM1
53      7 and 1/2       LM1
60      8 and 1/2       UP2, UP3, UP4, LP2
67      9 and 1/2       LP3
74     10 and 1/2       LP4, LM2
 
That is the only reliable way to get the approximate ages of kits.  If
those teeth are breaking through it's the approximate age.
(Source:  _Biology and Diseases of the Ferret_)
[Posted in FML issue 3732]