Puncuating a list of quesitons in a sentence

This is a tough question. It appears to be a matter of editorial style rather than a rule of grammar. Even so, the two guides I have handy this afternoon -- Chicago Manual of Style and MLA Stylebook -- do not address the question directly and provide vague and sometimes internally contradictory advice.  In both, I first tracked down all of the advice about question marks and then colons.

The best answer appears to be the sentence(s) is/are almost correct as presented. Because each of the questions is a complete sentence, and because the introduction is also a complete sentence, end "age-old quesions" with a period. Then you have four complete sentences, properly punctuated -- although the quotation marks are not necessary according to both Chicago and MLA.

" ... age-old questions. Who is man?  Why is he here?  What is the meaning of life?"

On the other hand, if the questions were all incomplete sentence fragments -- who? what? why? -- the style manual advice becomes even more vague. Chicago and MLA accept the use of an isolated sentence fragment, such as "why?" for emphasis. So a period after "questions" still would be appropriate.  But Chicago also suggests (and I didn't look in MLA) that a colon or em-dash could follow "questions" and the three question fragments would follow, but lower case.

" ... age-old questions. Who? What? Why?"  or " ... age-old questions: who? what? why?"

I like the way the second looks, but can offer no other justification for that preference.