They really got it right when they said 'the character formed at three stays till a hundred.'
Literal
Three-child [possessive-の] soul hundred [until-まで] [quotative-とは] truly well said thing [copula-だ].
三つ子の魂百まで is a famous proverb meaning 'the character formed by age three persists for life' — the Japanese equivalent of 'the child is father of the man.' ~とはよく言ったものだ is a set expression for admiring the wisdom of a saying: 'they really nailed it.'