幼い|おさないosanai[3]nakadaka (mid-high)

1. i-adjectivevery young; little
   その幼おさない少年しょうねんは父親ちちおやの両肩りょうかたの上うえに乗のっていた。↗

   The little boy sat on his father's shoulders.
2. i-adjectivechildish; immature
   彼かれの考かんがえはとても幼おさない。↗

   His way of thinking is very childish.

• Synonym幼稚ようちNeutralChildish and immature, mostly used to criticize ideas or methods, as in 「幼稚な考え」.
• Synonym稚いいとけないWrittenA written, elegant word for being young and innocent with a childlike air, as in 「いとけない子」.
• Related若いわかいNeutralThe general word for young, with a broad range that includes adults; 「幼い」 is for small children or a childish mind.
• Related年少ねんしょうWrittenA written-style noun for being young or underage, as in 「年少者」; also the youngest class in kindergarten.
• Related未熟みじゅくNeutralRefers to unripe fruit or a lack of skill and experience, as in 「未熟者」.
• Related年若いとしわかいWrittenA written word for being young in age, stressing youth itself; 「幼い」 covers very young children or a childish mind.
• Related未成熟みせいじゅくWrittenAn objective term for body, mind or abilities not yet fully developed; most often found in formal or written contexts.
• Related年若としわかWrittenA written-style word for being young; little used in modern Japanese.
• Related子供じみたこどもじみたNeutralSays an adult's words or behavior are childish, with a critical tone.
• Related子供っぽいこどもっぽいCasualColloquial; describes an adult as childish, in a tone that can be critical or simply neutral.
• Related子どもらしいこどもらしいNeutralPositive: having the innocence a child should have. 「幼い」 can be neutral or critical, as in 「幼い考え」.
• Related青臭いあおくさいCasualColloquial; criticizes naive, immature thinking with a mocking edge.
• Related乳臭いちちくさいCasualColloquial; wet behind the ears, said with contempt.
• Antonym老いたWrittenAntonym: a written-style word for having grown old, the opposite of 「幼い」 in the sense of young.

Use 「幼い」 for very young age or an immature mind. For simply young, including adults, use 「若い」. To criticize childishness pick 「幼稚」 or 「子供っぽい」; for lack of skill or experience 「未熟」; for a child's innocent charm 「子どもらしい」. 「稚い」「年若い」「年若」 are written-style words for youth, 「年少」「未成熟」 written-style nouns, and 「青臭い」「乳臭い」 mock the inexperienced.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 年齢ねんれい（生活せいかつ年齢ねんれい）が低ひくいこと。
2. 生活せいかつ年齢ねんれいに比ひして精神せいしん年齢ねんれいが低ひくいこと。子供こどもっぽい。