New Moon Bella and Jacob Rabbit Scene

What does Bella mean here, when she sighs and says that quote in bold?

"No way!" I shouted as I jumped out of the truck. "You're done! I can't believe it! You

finished the Rabbit!"

He beamed. "Just last night. This is the maiden voyage."

"Incredible." I held my hand up for a high five.

He smacked his hand against mine, but left it there, twisting his fingers through mine.

"So do I get to drive tonight?"

"Definitely," I said, and then I sighed.

"What's wrong?"

"I'm giving up—I can't top this one. So you win. You're oldest."

He shrugged, unsurprised by my capitulation. "Of course I am."