Kingdom of Knuffel

In the options for listing for your Knuffles, there is an option to list by Age Ascending or Descending. I do not see any Age Statistic on a knuffle's profile. Am I overlooking something somewhere or is this a hidden stat. It would be interesting to see a Knuff's exact age (I'm assuming since adoption which would kind of equal it's birth). Just wondering based on the option to rank that way, obviously the "birthdate" is known somewhere in the code.