Why is youthfulness often associated with foolishness

“Ben ducked beneath the arbor and paused by the fishpond when a memory crept upon him like a shadow. This was the spot where Alice had first read to him from her manuscript. He could still hear her voice, as if it had somehow been captured by the leaves around them and was being played back now, just for him, like a gramophone recording.
"I've had a brilliant idea," he heard her say, so young and innocent, so full of joy. "I've been working on it all morning and I don't like to boast, but I'm quite sure it's going to be my best yet."
"Is it?" Ben had said with a smile. He'd been teasing, but Alice had been far too excited to notice. She'd leapt on with telling him about her idea, the plot, the characters, the twist, and the intensity of her focus- her passion- changed her face completely, bringing an animated beauty to her features. He hadn't noticed she was beautiful until she spoke to him of her stories. Her cheeks flushed and her eyes shone with intelligence. And she was 'very' clever. It took a certain kind of clever to figure out a puzzle- to look ahead and see through all the possible scenarios, to be so strategic. Ben didn't have that kind of brain.
In the beginning he'd simply enjoyed her enthusiasm, the indulgence of being told a story while he worked, the chance to bat ideas back and forth, which was so much like play. She made him feel young, he supposed; her youthful preoccupation with her work, with the very moment they were in, was intoxicating. It made his adult worries disappear.”
― Kate Morton, The Lake House

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