Mycroft can't imagine going a year without visiting his brother, but it's obviously happened. And he's already come to understand that he lives long enough to strike a bad note with John. His mind fills in the rest, exaggerates the emotional changes he's already begun to feel and imagines the worst. "Old and grouchy," Mycroft repeats, eyeing Sherlock over the edge of his cup. "Can't imagine that set a good accord with your husband."
Thirty-eight. Mycroft's in quiet wonder about it all. His little brother is thirty-eight and married; he never thought he'd live to see the day. But here it is - and aside from Sherlock being all cracked around the edges and under the weather, he can honestly says that it suits him. "Last mission." And that's really all he's at liberty to say about it. And nobody needs to be a genius to say that it's going badly, but only Sherlock would probably know that Anthea's pulled him through so far.
And that her absence right now is a little hard on him - but at least his brother is here, alive and well. Upon hearing his brother's invitation however, Mycroft closes his eyes for a few seconds and reluctantly nods.