Hi so I used to think that "Señora" was if you were married only . . . but then I had to use it for a single older lady so I did "Señora" making me think it had to do more with age. So I tried it out on a 25 year old single lady and she objected and said it is Señorita (I think because it made her sound older than she was). I was curious how everyone uses it and if it is age dependent, what age you consider as the cut-off and if it varies throughout the Spanish speaking world. Right now my rule is to just call all women Señorita unless I know they go by Señora.