Sherlock smiles because Mycroft is smiling and his brother is always so indulgent of him.
"Actually, the last time I was in London was a year ago. And you were old and grouchy and we weren't on the best of terms," he says. But it's not this Mycroft. This Mycroft is the only person Sherlock ever loved until he met John Watson. This Mycroft, before the weight of the world broke him.
"Helped me move," Sherlock nods his head. "So I was thirty-three. You're forty," he adds with a smile. "Still with MI6. I'm thirty-eight," the smile doesn't fade, because there are weirder things to think about other than the fact that his brother has just gained five years back. "You should stay with us for a few days."