。
She's old enough to get a driver's license.
Literal
She [topic-は] car [possessive-の] driving-license [subject-が] can-get age [is-だ].
The phrase ~年だ ('is the age [where/that]') is a tidy idiomatic shortcut: literally 'she is the year [in which] one can get a license,' meaning 'she's reached the age where she can get one.' In Japan the standard car license (普通自動車免許) becomes legally available at 18; mopeds (原付) and small motorcycles (普通自動二輪) can be licensed from 16. Driving is much less universal among young Japanese than in the US — public transit covers most needs, especially in cities, and many adults never bother getting a license. The relative clause 自動車の運転免許が取れる ('can get a car driver's license') modifies 年 ('age, year').