What does the term early onset dementia means?

Hi! I heard that my cousin has symptoms of early onset dementia. I’m not sure that I know what early onset dementia is. I know that dementia is some can of disease. Bit it affect people who are elderly. Please, can somebody tell me What does the term early onset dementia means? Thanks!

The term early onset dementia (or younger onset dementia) is usually used to describe people under the age of 65 with any form of dementia. This term covers all symptoms of a large group of illnesses which cause a progressive decline in a person's mental functioning. As you know, dementia in younger people is much less common than dementia occurring after the age of 65.