What should I expect if I start talking to a 34 year old man that's extremely close to his 35 year old sister?

I'm 23 years old. The pic down at the bottom is him and his sister. I guess I'm asking because I'm not used to that type of sibling bond.
What should I expect if I start talking to a 34 year old man thats extremely close to his 35 year old sister?
What should I expect if I start talking to a 34 year old man that's extremely close to his 35 year old sister?
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