It seems that none of us have an Islaamic rule for you to follow. The closest rule to this I can think of is that we are to show respect to people in general, and our family members in particular. So my Phalasteenee nephews and nieces are particular about calling me Khalto. 'Amto is also used. My kids call their aunts on their father's side 'Amto. When young Arab children meet me, they call me Khalto. The reason for this difference is complicated, but it means almost the same thing.
When the young girls I used to teach who were not Arab got older, they felt confident in calling me Sister. But Arab girls in their 20s call me Khalto still because they would feel they were being disrespectful to me if they did otherwise.
Arabs call all old Muslim women Hajjee, and men Hajj out of respect, not out of the reality of whether or not they went on Hajj.
Another Islaamic fact: I know we are encouraged in the Hadith to call people by their kunya. A kunya is if your oldest child is William or Sasha, you would be Um-William or Um-Sasha. If it is Sara, you would be Um-Sara; However, the custom is that if the oldest child is a girl and then you have a boy, the boy's name is used. So Um-Sara might become Um-Ahmed even though Sara is her oldest. However, if you take your kids to different schools, the people at Sara's school can still respectfully refer to you as Um-Sara, because they don't know about Ahmed and they have a lot of kids to watch, so it's easier and still respectful to call you by something that is familiar and they can remember.
When I meet an older Arab woman I ask her name and sometimes she tells me her kunya and sometimes she tells me her name. I try to ask what she would like me to call her and I listen to what other people of different ages address her as.
People from other cultures have norms that I personally do not know. I just ask them what I should call them and listen for what other people do as well. They might tell me one thing thinking it is easier for me, but other people respectfully call them something else.
Al-Hamdulillah (From a Married Muslimah) La Howla Wa La Quwata Illa BiLLah - There is no Effort or Power except with Allah's Will.