Why do many people gossip around unmarried men or women over the age of 25 in rural areas?

Because it is in the countryside! Feudal thought, generally 18-year-old people who don't study urge marriage, and the possibility of studying will wait until you graduate! Old people want their children to get married and have children early, but people who get married early don't like being unmarried around the age of 25. To sum up, naturally there is gossip!