The average is exactly one value and nobody has exactly that value. Since average~mean 50 % are below and 50 % above average.

What you are talking about is a range that is around the average, specifically one standard deviation (=15 points) around the average/mean value, which is a completely arbitrary range and I do not know why you assign “average” to this range. 90 to 109 is a range I know to be attributed “average”, still arbitrary, but at least an actually established range.