The Doctor looked up when the girl came up to him, a smile tugging at the corners of his mouth. "You're never too old to play tag," he told her cheerfully, "never. Anyone who says otherwise is lying. Or dull. I think I'd prefer it if they lied." At least then they weren't being barmy old codgers, whoever 'they' were. He looked at the unfamiliar young woman, still smiling. "And anyway, wouldn't you be considered 'too old'? Yet here you are. It's not a bad thing, I'd say."