No, it is not appropriate at all. Sex stories are private and often inappropriate for general conversation, especially between an old lady and a mom. It goes against social norms of propriety and may make the mom uncomfortable.
It could be that the old lady has some old - fashioned ideas about sharing life experiences, including some inappropriate ones, without realizing the inappropriateness. She might have thought it was a normal part of sharing wisdom from her own life.
The mom could firmly but politely stop the old lady. For example, she could say 'I'm not comfortable with this topic, let's talk about something else'.
It's not okay at all. In most societies, there are clear norms about appropriate relationships. This kind of situation goes against the trust and respect that should exist in a relationship with a girlfriend, and it can lead to a breakdown of multiple relationships and a lot of emotional pain.
The age of the mom isn't explicitly mentioned. However, from her behavior and the family dynamics, she could be around 40. Her maturity and role in the family suggest she's at a prime parenting age.
The age of the mom isn't given precisely. However, based on the context and her family situation, one could guess she might be in her late 30s to early 40s. Her character is depicted as a mature and caring parent, which often suggests a certain age range in such stories.
No, it is not appropriate at all. Such topics are private and often considered inappropriate to discuss with parents. It can make both you and your mom feel extremely uncomfortable.