Canonical hadiths say Muhammad (in his fifties) consummated his marriage to Aisha when she was nine (lunar) years old

A lunar year is about 355 days long, which means that at consummation, Aisha may actually have been as young as 8 years and 9 months old (in 365-day years).

Some examples from al-Bukhari, the most canonical hadith collection:
Sahih al-Bukhari, Volume 7, Book 62, Number 64:

Narrated 'Aisha:

that the Prophet married her when she was six years old and he consummated his marriage when she was nine years old, and then she remained with him for nine years (i.e., till his death).

_____________________________

Sahih al-Bukhari, Volume 7, Book 62, Number 65:

Narrated 'Aisha:

that the Prophet married her when she was six years old and he consummated his marriage when she was nine years old. Hisham said: I have been informed that 'Aisha remained with the Prophet for nine years (i.e. till his death)."

_____________________________

Sahih al-Bukhari, Volume 7, Book 62, Number 88:

Narrated 'Ursa:

The Prophet wrote the (marriage contract) with 'Aisha while she was six years old and consummated his marriage with her while she was nine years old and she remained with him for nine years (i.e. till his death).

_____________________________

Sahih al-Bukhari, Volume 5, Book 58, Number 236:

Narrated Hisham's father:

Khadija died three years before the Prophet departed to Medina. He stayed there for two years or so and then he married 'Aisha when she was a girl of six years of age, and he consumed that marriage when she was nine years old.