The voting rate of elderly people is higher than that of young people.
elderly people高齢者
young people 若者
The voting rate of elderly people is higher than that of young people.
で、高齢者の投票率と若者の投票率を比較していますが、投票率を二度言う必要はなくて、that of young peopleというほうが自然です。thatが投票率のthe voting rateを指します
日本 
