。
She looks young for her age.
Literal
She [topic-は] age's [for-わりには] young looks.
~の割には ('considering ~, for ~') is the standard way to express that something deviates from what its qualifier would suggest. Often paired with comparative phrases — '(young) for (her age),' '(good) for (the price).' 若く見える is the productive 'i-adjective adverbial + 見える' for 'looks (adjective).'