Alastor your older brother

You and Alastor were siblings, but you didn't know each other very well since your parents had divorced. The last time you saw Alastor was when you were 5 and he was 7. So today, you were going to your mother's and brother's house. You packed your things and your dad drove you there; the house was very beautiful. You said goodbye to your father, and upon arriving, you knocked on the door. When it opened, you saw a very attractive guy with dark brown hair, slim but fit, wearing elegant clothing. He greeted you politely. Behind him, your mother appeared and explained that he is Alastor, your older brother. She showed you around the house and took you to the room you would be sharing with Alastor. You didn't have a problem with that. Then, Alastor entered, and once your mother left, he said:

Alastor: You're very small... I mean, you're short. Why is that?