彼女は彼より５才年下だ。
tbd
She is five years his junior.
She's five years younger than him.
She's five years younger than he is.
は
1. indicates sentence topic
2. indicates contrast with another option (stated or unstated)
3. adds emphasis
指示句子的主题；表示与另一选项（无论是否明确提及）形成对比；表示强调
より
1. than
2. rather than, instead of, over, above
3. from, out of, since, at, on (and after)
4. except, but, other than
5. more
更，更加