question for experts on Disney animatores about nine old men

Ok, I'll take a shot at this - though don't take this as definitive!

I don't know when Disney actually made the reference to his top animators, likening them to the Nine Old Men that made up the Supreme Court (the phrase comes from the title of a book about the Justices, all of whom were over 70, written by Allen and Pearson and published in 1937: Disney's use of it was maybe in the 50s?). Several other animators had been key in establishing the Disney animation style - Bill Tytla, Freddie Moore, Norm Ferguson, Art Babbit, for example - but these nine were the men who had become Disney's prime animators by the 50s.

They are, roughly in order of joining Disney's: Les Clarke (joined 1927), Eric Larson, Wolfgang Reitherman (both joined 1933), Milt Kahl, Ward Kimball, Frank Thomas (all joined 1934), Marc Davis, Ollie Johnston and John Lounsbery (all joined 1935).

They had impressed Walt, with their work, their ideas and analysis, and with their personalities, and were the animators deemed good enough to work on the features, which required the best animators. The reasons for this favoritism, although primarily based on quality of work, were varied and idiosyncratic, based on Walt's personal feelings. It is not insignificant that many of the Nine had stayed at their desks rather than coming out on strike in 1941.

The training system, that had started in the mid 30s, had now evolved into putting would-be animators, who had passed basic training, under the supervision of a senior animator - first as an in-betweener and then as an assistant animator. This led to the Nine Old Men becoming heads of animation 'units' with a small team of animators under them when working on features. So sequences were allotted to the Nine, who attended the story meetings, and these were then broken down within the units, the 'lesser' animators doing many of the scenes under the supervision of the lead animator, who concentrated on the most important 'personality' scenes. (The lead animator having already done experimental animation on a few scenes to establish the character, poses from which would make up the model sheet used throughout the film.)

As years went on and Disney's interest shifted from animation to live action and the theme parks, the Nine (or rather, those of them who still remained!) took greater charge of the animated features, their positions now cemented in the studio structure.

My answer was not to be taken as definitive since, although the general sweep of my answer went some way to answering the question, there were bound to be factors I had forgotten or not known about at all. (I am a Disney fan, not a historian!) The trouble is that from the 30s until the end of the 50s the production methods of Disney's studio had been undergoing constant evolution - shifting constantly as Walt demanded different goals: efficiency on the one hand and creativity on the other. Therefore Disney's 'production method' is bound to be hard to pin down - what is true on the early features is no longer the case on later features, etc.

A better answer may be this quote from an article by Sheila Hagen (on the demise of Frank Thomas, in 2004):

"During the 1930s and early '40s, there were many attempts to try to organize and improve the operations of the studio, but it usually resulted in the creation of factions and a feeling of divisiveness and isolation amongst the artists. Walt Disney tried to counteract this by creating an animation board in 1940 to oversee the division of work at the studio, and by 1950, the board was permanently set to consist of nine veteran animators.

These nine men—Les Clark, Marc Davis, Ollie Johnston, Milt Kahl, Ward Kimball, Eric Larson, John Lounsbery, Woolie Reitherman and Frank Thomas—were facetiously dubbed the Nine Old Men after the nine judges sitting on the Supreme Court.

Thomas and Johnson joked about this title in their book, The Illusion of Life – Disney Animation:

“We never thought of ourselves as some elite group, and the only time it even crossed our minds was when Walt made a kidding remark about his Nine Old Men being over the hill, or getting too decrepit to work, or losing all their old zip.”

Along with the finalization of the membership of the Animation Board, an important change occurred in how animation jobs were assigned. Previously, many animators would work on the same character, depending on who was available at the time. Although efficient scheduling-wise, it meant that there never would be true continuity for any character. By assigning one animator to work on one character, it guaranteed that that animator could fully explore the character's personality and emotions, resulting in a higher quality of realism."​

~ Howdy, Folks!

Just to chime in here with my own two-cents. There is one all important thing that you've been overlooking about the Nine Old Men. Unconditional and unwavering devotion and allegance to Walt Disney. These guys spent their entire creative lives at the studio because it was Disney! They never left his side. You can chart the special magic these individuals brought to the films in release after release. Their special talents and unique experience were acquired after many years at the studio. In the 1970's Disney found itself in dire straights when the Animation Department was being neglected and the Nine Old Men were starting to retire. Almost too late Disney realized it might be a good idea to train the next generation of Disney animators while they could still benefit from the presence of some of the Nine Old Men.