One of only two mice to successfully escape from the NIMH laboratory, Mr. Ages developed a talent for chemistry, medical sciences and biology, and has used these skills, and his great knowledge, as a physician for the wild animals living on and near the Fitzgibbons farm.  Known for his crusty, acerbic and superstitious nature, he prefers to keep to himself and be left alone, living on the fringes of the Fitzgibbons farm in an old (and not entirely deactivated) hay baler.  He makes frequent visits, however, to the rose bush and the colony established by the rats of NIMH, and serves there as a senior and influential member of the community.  Despite his personality quirks (and his often harsh opinions of others), he is very fond of the Brisby family, and is completely dedicated to the rats of NIMH.

Quote: "Madam, that is an emergency!"

Origins of the character: In Robert C. O'Brien's book "Mrs. Frisby And The Rats Of NIMH", Mr. Ages is not quite the acerbic old fusspot he is in the movie (though he is older than the other mice, and many of the rats).  He is not described in much detail in the book: "His fur was a soft gray-white, and so glossy he seemed almost to glow.  Mrs. Frisby had heard that Mr. Ages was not truly a white mouse; that is, he had not been born with white fur, but had turned white from old age.  Whether this was so or not she did not know.  Certainly he seemed very old, and very wise; yet he walked nimbly enough."

In the book, Mr. Ages' living quarters (and his private laboratory) are also quite different than in the movie.  Mr. Ages is said to live in the corner of the brick foundation of an old, burnt-down farmhouse.  As described in the book, Mr. Ages’ house was “a hole in the brick wall where one end of heavy floor beam had once rested.  It was about two feet below the top of the wall, and one reached it by climbing down a sort of rough stairway of broken brick ends…”, with a door “…made of a piece of shingle”, with a “…narrow ledge of brick in front of [the] door”.  The house, “…somewhat larger than a shoebox but about the same shape, resembled the house of a hermit.  It was bare of furniture except for a bit of bedding in one corner, a stool made of a piece of brick, and another piece of brick worn smooth from use as a pestle on which he ground out medicines.  Along one entire wall, arranged neatly in small piles, stood the raw materials he had collected: roots, seeds, dried leaves, pods, strips of bark and shriveled mushrooms.”

In the animated sequel: In the sequel, Mr. Ages plays an active role in the Thorn Valley community, almost as a co-leader with Justin.  He's even seen in their council chamber in the primary seat of authority.  We also see him cataloging local flora and fauna, as well as tutoring and advising young Timothy Brisby.  It seems that, in the sequel, Mr. Ages has picked up and left his home in the old hay baler and moved permanently into the Thorn Valley community, along with all of his laboratory equipment.  Apart from that, and the fact that he appears to have lost a lot of his endearing personality quirks (at least in how he is presented in this sequel), there are no changes to the character whatsoever.