The shape of the character 瓜 can be decomposed into two 八 (“eight”), thus “breaking 瓜” is used to refer to reaching the age of 8+8 (=16) for girls, and 8×8 (=64) for men. First attested in the 4^th century.

破瓜

1. (literary, of a girl) to reach the age of 16; to come of age

   • 妾身李貞麗，只因孩兒香君，年及破瓜，梳櫳無人，日夜放心不下。
     妾身李贞丽，只因孩儿香君，年及破瓜，梳栊无人，日夜放心不下。

     From: 1708, Kong Shangren, The Peach Blossom Fan, translated by Xu Yuanchong

     Qièshēn Lǐ Zhēnlì, zhǐ yīn hái'ér Xiāngjūn, nián jí pòguā, shūlóng wúrén, rìyè fàngxīnbùxià.

     I am Mother Lee. My daughter Fragrant has come of age and I am worried day and night to find for her a life companion.

2. (literary, euphemistic, of a girl) to lose one's virginity
3. (literary, of a man, rare) to reach the age of 64

• 破身 (“to have sexual intercourse for the first time”)
• 開瓜／开瓜 (“to take a woman's virginity”)

Japanese Wikipedia has an article on:

破瓜

Wikipedia ^ja

Similar to the sense development of Chinese 破瓜 (pòguā), the shape of the character 瓜 (literally “gourd”) can be 破 (“broken”) or decomposed into two 八 (“eight”) characters, thus “breaking 瓜” is used to euphemistically refer to reaching the age of 8+8 (=16) for girls, and 8×8 (=64) for men.

The girls' age sense is cited to the late 1600s. The men's age sense is cited to the early 1700s. The sexual sense is cited to the late 1800s.

• (Tokyo) はか (Atamadaka – )
• IPA^(key):

破(は)瓜(か) • (haka) ^{←はくわ (fakwa)?}

1. the age of 16 for a girl
2. the age of 64 for a man
3. (by extension from the age 16 sense) the breaking of the hymen through sexual intercourse
4. (by extension from the age 16 sense) hebephrenia, disorganized schizophrenia: a type of schizophrenia with onset typically occurring during adolescence

   Synonyms: 破瓜病 (hakabyō), 破瓜型総合失調症 (haka-kei sōgō shitchō-shō)

• 破(は)瓜(か)期(き) (hakaki): adolescence, puberty
• 破(は)瓜(か)病(びょう) (hakabyō): hebephrenia