。
She's much older than him.
Literal
She [topic-は] him [than-より] far age-above is.
ずっと is an intensifier — 'far, much, by a long way' — used both with comparatives (ずっと年上, 'much older') and with continuous time spans (ずっと前, 'long before'). 年上 ('older,' literally 'years-up') and 年下 ('younger,' 'years-down') are the standard age comparison nouns; they function as predicates with the copula. The である copula stamps this as written/formal register; in casual speech you'd hear 年上だ.