Multilingual individuals exhibit brain structures that are, on average, 6 to 13 years younger than those of monolingual adults.

Study: Use of multiple languages provides cognitive reserve amidst age-related white matter changes.

People who speak multiple languages have brains that look more worn out on scans, but they still think just as well as people who speak only one language — like their brains are acting younger than their actual age.

Study: Multilingualism protects against accelerated aging in cross-sectional and longitudinal analyses of 27 European countries

People who speak more than one language tend to have bodies and brains that age more slowly than those who speak only one language, according to a huge study of nearly 90,000 people. This suggests their brains might look younger than their actual age.

Study: How age of acquisition influences brain architecture in bilinguals

People who learn a second language early have bigger brain areas linked to language and memory, which are usually smaller in older people — so their brains look younger. This doesn't prove their brains are exactly 6–13 years younger, but it shows a strong link between speaking more languages and healthier brain structure.

Study: Age-Related Differences in Speech and Gray Matter Volume: The Modulating Role of Multilingualism

People who speak more than one language have brains that look younger than those of people who speak only one language — their brains don’t age as fast, especially in areas used for speaking.