it changes throughout our lives based on numerous things.
the type/brand of insulin can even be a factor. As an example, for me, i use the least amount of insulin with Apidra, A little bit more (about 25% more) with Novolog, but have a very high resistance to Humalog.
Temerature, time of year, time of month (for women), diet, level of regular physical activity, etc. ALL play a part in our sensitivity to insulin.