Regulus couldn't completely contain the look of surprise that crossed his face, but he did manage to squash it down fairly quickly upon hearing his older brother's voice. Oh, fantastic. This was just what he needed: a little judgmentalism sprinkled on top of his anguish. The younger Black gave his brother a brief glance, taking in the fact that he was much younger than Regulus had anticipated after reading those books, then turned back to his glass. He gave it a much more thorough looking over before shrugging an answer to Sirius. "I'm 18. It's legal as far as some of the Muggles are concerned."
He sighed, the expression on his face becoming sour, and took another deep sip of the scotch. "Look, brother," he began, his voice sarcastic. "If you're here to shout at me, could you get on with it? As you can see, I'm quite busy. I'd like to spend some of my night in peace." If this conversation was headed in the direction that Regulus both guess and dreaded that it was going, he would rather get it out of the way as quickly as possible so that he could go back to pretending he didn't know anybody here.