[he doesn't understand why she looks like she's about the cry, even while smiling. Well, no, that's a lie. He totally understood how it felt sometimes to be happy enough to want to cry. He just doesn't understand how his answer could have brought that sort of reaction]

20? [but he smiles back at her anyway] Could've fooled me!

And yeah, the weather's not too warm and not too cold during May... Golden Week too! That's always a good time to set up get togethers for the team.