Which sentence is correctly punctuated?

The correct sentence effectively uses punctuation to convey meaning clearly and accurately. It includes the contraction "It's," which stands for "it is," correctly indicating possession and contractions. The phrase "twenty-year-old" is also properly hyphenated, as compound adjectives preceding a noun are typically hyphenated to avoid confusion and ensure clarity. Additionally, the phrase "up to date" is correctly used without hyphenation since it functions as an adverbial phrase rather than an adjective modifying the noun.

The other options either misplace punctuation or miss the correct form of a word, which can lead to confusion or misunderstanding. For example, using "its" instead of "it's" changes the meaning, as "its" is a possessive pronoun. Additionally, omitting the hyphen in "twenty year old" or misplacing commas can affect the readability and grammatical accuracy of the sentence. Thus, the proper use of punctuation and language conventions is what makes the first sentence the best choice.