"We've spent quite a bit of time together since I came to see you on Dragonstone." True, they'd both wanted something out of it, but they'd also both gotten what they were looking for.

"I'm the oldest of the Starks still living." Which doesn't mean he's not young. It just means there's no one else to go to for this, and protecting the North is now his responsibility. Even if he's not a Stark by name. "I was born not long after Robert's Rebellion ended." Which gives her an idea of his age, and how it compares to hers.