Is it permissible to visit my brothers house although im not married?

My brother (in his late twenties) recently moved out of my parents house. I (female, in my early twenties) thought this was not a big deal as I thought I could visit him. However my parents said I can’t go to his house on my own until I'm married because it’s not permissible in Islam. When I tell them to elaborate they tell me I won’t understand. I really don’t understand how visiting my own brother isn’t permissible in Islam, if it was a male friend I would totally understand but this is my brother. I don’t think my parents would lie and if they aren’t I need a clear explanation.