User blog comment:Argulor/Characters ages/@comment-8072-20130723040500

One season does not equal one year (this is covered on the Seasons article).

Also, Matthias may be interpreted by some readers to be 13 in human years, but this has never been stated by Mr. J (to my knowledge), so that's not definitive by any means.

Finally, the argument can be made that mice and birds mature differently. A mouse who is five seasons old could actually be much younger than a bird who is five seasons old.