Very few people live to be a hundred.

Literal

Hundred years [until-まで] living person [topic-は] hardly exist [polite-ません].

ほとんどいません means 'there are almost none' — the polite negative of いる with ほとんど. まで marks the endpoint of living ('to/until'). 百歳 (ひゃくさい) is 'one hundred years old.'