Translation guide
The concept of a person's mental ability expressed as the age at which an average person reaches that same ability. In Japanese, this is typically expressed using the term 精神年齢 (seishin nenrei), but the concept can also be conveyed through descriptions of maturity or childishness.
The standard psychological concept of mental age, often used in testing or clinical contexts.
Describing someone's behavior or personality as being like a certain age, often implying immaturity or precociousness.
精神年齢 (mental age) is often contrasted with 実年齢 (actual/chronological age) or 肉体年齢 (physical age). In casual conversation, 精神年齢 is the go-to term for discussing maturity levels.
There's a big gap between mental age and actual age.
The direct translation and standard term for 'mental age' in psychology and education.
His mental age was assessed as 10 years old.
A less common synonym for mental age, literally 'intelligence age'. Used in some psychological contexts.
Mental age does not necessarily match chronological age.
He's an adult but has a low mental age.
Literally 'mental age is high', used to say someone is mature for their age.
She's still young but has a high mental age.
Pattern to specify a mental age, e.g., 精神年齢が5歳 (mental age of 5).
That person's mental age is at an elementary school level.
Literally 'inside is a child', a common way to say someone is childish despite their age.
He's big in body but a child inside.
Means 'immature' or 'childish' for an adult. Implies low mental age.
Getting angry over something like that is so immature.
While 精神年齢 is understood, in very casual conversation, phrases like 中身は子供 or 大人げない may sound more natural than directly saying 精神年齢が低い. Use 精神年齢 when you want to be precise or slightly analytical.