No two chins and no two shoulder are the same, yet between them violin and viola players need to hold their instruments with comfort and stability AND also allow the violin to vibrate.
Fortunately there is a plethora of shoulder rests and chin rests available today to support players individual needs, for which I keep a good range for adult and developing bodies.
Young bodies are especially challenging, often neck length is short and so super low chin and shoulder rest combinations are required…of course in a years time – just like a pair of shoes something bigger might be required.