There was a time when couples used to prostrate before the elders to seek their blessings. In turn the elders would say to the lady in front of them 'dheerga sumangali bhava' literal meaning "May you live longer as a married woman" What so funny about it ? According to Hindu tradition a married woman should exhibit certain features like wearing a mangalsutra around her neck applying kum kum on the forehead and at the centre partition of the hair , wearing metti (a sort of an ornament) on the second toe of both legs and flowers decorating the back of her head .
These days it is very difficult to distinguish a married woman from an unmarried woman. Nowadays, neither the marriages are made in heaven nor marriage of convenience it is purely called marriage of connivance. Hence, it is irrelevant to be blessed to be an eternal sumangali.
There is a rider in that blessings one may call it a hidden agenda of the male dominated world. Another meaning to the blessing is let the wife predeceases her husband. In that case menfolk, would expect such blessings from the elders very often.