In this case, is "little" being used, like you would in English, to mean "younger," or does it strictly refer to the actual, physical size of the person?
Would "òg", as in young, be uncommon? Or could this even be understood as a very young child?
If you were trying to explain to someone that you had a young sister, then yeah, you'd use òg. But if you wanted to say you had a younger sister, then beag would make more sense.
Either or in this case, although it would probably be understood as referring to a younger sister.
Why doesn't 'I have a small sister' work?
I can't remember why this is bheag vs beag
I am also unclear about whether this would apply to size