Menopause is achieved when there are no periods since a year. Average age of menopause in the world is 51. Typically in the transitional phase ( lasts anywhere between 2 to 4 years), one faces irregular periods , sudden hot flashes in the face and body, sweating at night. Some women feel vague pains and aches, fatigue and disinterest in daily activities.  But irregular periods is the most likely symptom even if it happens once or twice a year preceeding menopause. There are certain blood tests to check for it but they are not more reliable than the clinical symptoms

The average age for menopause is 50 years but it could happen much earlier too. Periods becoming irregular around this age is a tell tale sign.