Question

Which of these sentences is correctly punctuated you are old grandpa William said the young man

Answer 1

Please post the full question.

Answer 2

By "sentences," I assumed you meant "words," so it that spirit, the answer is:
"You are old, grandpa William," said the young man.
See, the young man is the one saying it, and the parentheses and comma clarify what the sentence is saying.

Answer 3

Actually, the grandpa's name should be "Grandpa William," because this is his title, so both should be capitalized. :)