No. In most ethical and moral frameworks, it is not appropriate for an older woman to seduce a boy. Such relationships often involve power imbalances, and the boy may not be fully mature enough to make consensual decisions in a truly equal way.
There are probably some in the realm of certain adult - themed fictional works. But these are not the kind of stories that are promoted or widely available in the mainstream. In fact, we should be more interested in stories that show healthy interactions between genders, where both parties are treated with respect and dignity rather than focusing on such erotically - charged and unequal relationship stories.
It could also be about maintaining social or family order. In a story set in a traditional society, a strict woman may dominate boys to ensure that they grow up to fit into the expected roles. She might spank them when they deviate from the norms, like not studying hard enough or being disrespectful. This is to keep the family or community's reputation intact and ensure the boys' future success in that social structure.
One negative impact is that it can desensitize people to the idea of abuse and domination. It may also set a bad example for young readers, leading them to believe that such extreme and inappropriate power imbalances are normal in relationships. Moreover, it can contribute to a negative perception of women as being sadistic, which is unfair and inaccurate generalization.
No, it is not ethical. Any form of dominance over minors in such a context is inappropriate and can be considered a form of abuse. Literature should promote positive values and healthy relationships, not something that involves the domination of the vulnerable.
In modern media, such stories can have negative implications. They may promote an unbalanced view of gender relations. It can also be seen as objectifying both genders in a sexual way.