Translation guide
The English word "immature" covers a range of meanings from biological underdevelopment to childish behavior. In Japanese, different words and expressions are used depending on whether you mean physically unripe, emotionally childish, or lacking experience.
Describing a person whose behavior, attitude, or emotional reactions are like a child's, often in a negative sense.
Literally 'unripe', this is the most direct and common translation for 'immature' when referring to a person's character, skills, or emotional development. It can be used in both formal and casual contexts.
彼はまだ精神的に未熟だ。
He is still emotionally immature.
そんな未熟な考え方は捨てなさい。
Get rid of such immature thinking.
Means 'childish' or 'infantile'. It carries a stronger negative connotation than 未熟 and is often used to criticize someone's behavior as puerile or silly.
彼の幼稚な行動には呆れる。
I'm disgusted by his immature behavior.
そんな幼稚な言い訳は通じないよ。
Such a childish excuse won't work.
Literally 'lacking adultness', this is used when an adult acts in a way unbecoming of their age. It implies the person should know better.
彼の反応は大人げなかった。
His reaction was immature.
大人げない喧嘩はやめよう。
Let's stop this immature fight.
Means 'childish' or 'like a child'. It can be neutral or negative depending on context, but often implies immaturity in a less harsh way than 幼稚.
彼女はまだ子供っぽいところがある。
She still has some immature traits.
Describing plants, animals, or body parts that are not yet mature or ripe.
The same word as above, but applied to physical immaturity. It can describe unripe fruit, undeveloped organisms, or immature cells.
この果物はまだ未熟だ。
This fruit is still immature.
未熟な細胞が分化する。
Immature cells differentiate.
A more explicit phrase meaning 'not mature'. It is often used in biological or technical contexts.
この動物はまだ性的に成熟していない。
This animal is still sexually immature.
Literally 'blue/green', but can mean 'unripe' for fruit or 'inexperienced' for people. For physical immaturity, it's mainly used for unripe fruit.
Describing someone who is new to a job, activity, or field and hasn't yet reached full competence.
Again, 未熟 is the go-to word. It can refer to insufficient skill or experience in a professional or artistic context.
私の技術はまだ未熟です。
My skills are still immature.
未熟な選手だが、将来性がある。
He's an immature player, but has potential.
Describing something abstract like a concept, proposal, or artistic work that is still in an early, unpolished stage.
Once more, 未熟 is versatile enough to cover this meaning. It suggests the idea or work needs further refinement.
その計画はまだ未熟だ。
The plan is still immature.
未熟な理論だが、興味深い。
It's an immature theory, but interesting.
Means 'under development' or 'developing'. It is often used for fields, technologies, or countries, but can apply to ideas that are not yet mature.
この分野はまだ発展途上だ。
This field is still immature (developing).
Literally 'incomplete'. It emphasizes that something is not finished, which can be a form of immaturity for creative works.
未熟 (みじゅく) is the most versatile and neutral word for 'immature'. It can be used for people, skills, ideas, and physical immaturity. 幼稚 (ようち) is specifically for childish behavior and carries a negative, critical tone. Use 未熟 when you want to state immaturity as a fact or lack of development; use 幼稚 when you want to call someone's actions puerile.
彼は未熟だが、努力している。
He is immature, but he is making an effort.
彼の幼稚な態度には我慢できない。
I can't stand his immature (childish) attitude.
The loanword イマチュア (imachua) is rarely used in natural Japanese. It might appear in some contexts like music genres or specific jargon, but it is not a standard translation for 'immature'. Stick to the native Japanese words above.
彼のその話題に対する理解はまだ未熟だ。
His understanding of the topic is still immature.
その果物は食べるには未熟すぎる。
The fruit is too immature to eat.
You can't eat immature (green) bananas.
Literally 'lack of experience'. This is a more specific way to say someone is immature due to insufficient experience.
彼の失敗は経験不足のせいだ。
His failure is due to immaturity (lack of experience).
Means 'half-fledged' or 'not yet a full-fledged person'. It implies someone is still learning and not yet fully capable. Often used humbly about oneself.
私はまだ半人前の職人です。
I'm still an immature (half-fledged) craftsman.
その小説はまだ未完成だ。
The novel is still immature (unfinished).