Translation guide
In Japanese, expressing 'become senile' ranges from clinical terms to everyday expressions. The most common and natural way is using the verb ぼける (bokeru), which covers age-related cognitive decline. More formal or medical terms exist, but are less common in daily speech.
To describe someone becoming forgetful or confused due to old age, in everyday conversation.
The most common and natural verb for becoming senile or demented. Used in casual and neutral contexts. Intransitive.
My grandmother has started to become senile recently.
Everyone becomes a little senile as they get older.
Same as ぼける but written with kanji. Slightly more formal or literary feel, but still common.
My grandfather has become senile and doesn't recognize me.
Literally 'to get dementia'. This is the clinical term and is used in formal or medical contexts. It is more direct and less colloquial than ぼける.
My mother has developed dementia and needs care.
Means 'to age' or 'to grow old', and can imply senility in context, but is not specific to cognitive decline. More literary.
When you become old and senile, obey your children. (proverb)
To emphasize a more serious state of mental decline, often with behavioral changes.
To describe the early stages of senility, often just forgetfulness.
Literally 'forgetfulness becomes severe'. A common way to describe early senility without using the word 'senile'.
Lately, I've been getting more forgetful.
A softer way to say 'starting to become a little senile'.
It seems my father is getting a little senile too.
The English phrase 'become senile' is often translated directly as 老人性認知症になる, but this sounds overly clinical and unnatural in daily conversation. Use ぼける instead.
He became senile. (unnatural, too clinical)
ぼける is the everyday verb for becoming senile, while 認知症になる is the formal medical term for developing dementia. Use ぼける in casual speech and 認知症になる in official or medical contexts.
My grandmother developed severe dementia and is bedridden.