Last year they hadn't really celebrated Remus' birthday -- probably because they'd been circling around each other anxiously at the beginning of everything. There'd been a lot of crying and all that, what with their terrible future and how Remus was from that. After that -- well, it'd been done and over by the time the tears had stopped and the flirting had begun.
But this year was a new year, and Sirius thought they'd had a pretty spectacular date full of romps and cuddling the night before. So now they could have a lazy birthday for Remus. Or, well, whatever kind of birthday he wanted. Obviously. Sirius was going to dedicate his day to making sure Moony got whatever Moony wanted. Nope, nothing selfish on Sirius' part at all. Just Remus pandering.
"You're old now," he said cheerfully, cuddling up more, pressing his chin a little more firmly against the top of Remus' head. He could do with a longer nap, maybe, but that didn't stop Sirius from being energetic anyway. But Remus was old. Or, at least, older than Sirius, which was sort of still weird to think about now and again, when they'd once only been a few months apart in age.