Why do courts consider a woman who reaches 25 years of age an "old maid" (عانس), what is the reason for this designation and what is meant by it, and what is its benefit?

In the Arabic language, an 'ānis' (spinster/bachelor) is someone who has delayed marriage after reaching maturity. This term applies to both men and women, although its use for women is more common. It is a linguistic term, not a Shariah-specific one. If a court designates a specific age, such as twenty-five, as the age of an 'ānis,' it is merely a conventional designation.