The difference is that a man at age 35 can start a family and have the first healthy child, which is not uncommon. For a woman at this age, it is already too difficult to physically carry a child, the likelihood of giving birth to a dawn or some other ugly one is very high. Therefore, an adult single woman without children is considered as non-liquid, and a man is not.
__________________
This is what the former Soviet Union believes. I live in one of the European capitals, and women just start thinking about children after 35! No one considers them illicit.