There’s still a lot of folklore about old violins, violas and cellos that go on and on about ‘old’ always being better and just by that nature (of just being old) should somehow substantially improve the quality of the instrument. Violas tend to be more of an evolved instrument than that of a violin. In the last century, even the last 50 years, violas have become more uniform in size than the century before. Still though, like the upright bass, there is no one specific size. Violins on the other hand are very close in feel and size. Violas can range from 15-17″ back lengths and can cause lots of hand, shoulder, neck issues to play instruments that are too big. Today, a new viola will be more geared to all these considerations. The selection of really great old, pedigree violas with a desirable size are very hard to find and afford. The newer violas are ‘smarter’ in that they were made with modern considerations of playing styles, repertoire and the type of strings that are used today.
Additionally, old violas made with tops that are too thick, or just inferior materials will never achieve the tonal characteristics because these aspects prohibit this.
Responsiveness and new instruments. Of course when it comes to a viola being played over many years, it is hard to compare that to a brand new viola. Just like a brand new baseball mitt that has never been used or broken in, the wood (especially the top) of a new viola has to be played in. The misnomer here is that some thing (wrongly) that it just gets better and better with each year. Even wine will get sour if left too long! Some actually think that the older instruments can be overplayed or overused too much over the years and need a break. This again, is mainly folklore.
The break in time for a new instrument is greatly noticed the first few years of the instrument (especially that first year or two) and again depends on the player. How he/she plays on it, how much, how hard.