If you look at the WHO and UN, the elderly is usually referred to in terms of 60+ or 65 +

If you are looking at women immediately post-menopause they are likely to be under this, I would suggest middle age or in terms which describe your participants. eg women who are over 50 years? Or women who have not had a period in the last 24 months (aged x to y, years).

Categorizing postmenopausal women as elderly in research settings may not be reasonable in the given backdrop of UN and WHO directives indicating men and women having attained the chronological age of 60 or 65 as elderly. In my opinion, referring to them as middle-aged would also be illogical and unconvincing. Commonly used terms such as premenopausal, postmenopausal and peremenopausal denote ageing women around natural menopause. In contrast to surgical menopause, natural menopause, in all probabilities, truly depicts the age at which a women experiences complete cessation of ovarian functions.To be precise, menopause,so to say, reproductive senescence brings forth abrupt and complete loss of fecundity.

Quite notably, loss of thymus commences quite early in the life of an individual.But human subjects with atrophied thymus are not considered as elderly. It is really very difficult to say with confirmity that exactly at what age of an ageing individual senility sets in.However, majority of authors suggest that good number of structural deformities and functional disabilities arise in sixties enhancing the risk of morbidity and mortality manifold.