expression, noun
age at which even the slightest things seem funny; giggly age
A set phrase describing the period (especially late teens for girls) when everything seems hilarious. Often used lightheartedly or nostalgically.
あの子は今、箸が転んでもおかしい年頃だね。
She's at that age where even the slightest thing makes her laugh.
箸が転んでもおかしい年頃だった頃を思い出すと、懐かしい気持ちになる。
Remembering the time when I was at that giggly age makes me feel nostalgic.
お年頃 refers generally to a marriageable or coming-of-age period, while 箸が転んでもおかしい年頃 specifically highlights the tendency to find everything funny.
Literally 'the age when even chopsticks rolling is funny'. A humorous, idiomatic expression; the exact origin is uncertain, but it vividly captures the heightened sensitivity and giggliness of adolescence.