十代

1. Origins, structure, and basic meaning

• Structure: 十代 (じゅうだい) is a noun for the ages from thirteen through nineteen in English-oriented translation, or more literally the second decade of life in Japanese use.
• Basic usage: 十代の頃 modifies the period when diary writing began, while 十代を対象にする makes that age group the intended audience of a reading club.

2. Common pitfalls and similar expressions

• Life period and age group
  • 十代の頃 is a period in one person’s life, whereas 十代を対象 denotes people in that age range collectively. It should not be narrowed to one exact age without context.