She tried to make herself look much younger than she really is.
Literal
She [topic-は] age [than-より] [a-lot-うんと] young show [tried-to-ようとした].
うんと is an adverb for emphatic 'a lot, much' — slightly casual, often heard in spoken Japanese. ~より sets up the comparison ('than her age'). 若く見せる is the productive 'i-adjective adverbial + 見せる' for 'make (oneself) look ~.' ~ようとする marks the attempt — possibly unsuccessful.