It is common to see a cup company state these guidelines. However, these guidelines have nothing to do with cervical height and may pose a problem when the user tries a size that might not be right for them.
It is believed that a person under the age of 30 that has not had any pregnancies, may have more toned PFM, or are “tighter” and thus need a smaller size.
While those over the age of 30 who may have had pregnancies or children, have a weakened PFM, or are “looser” and thus need the larger size.
While the PFM may weaken with age, weight, pregnancies, etc., Kegel exercises may be done to help tone them once again.