leo wrote:One legacy of Madison Avenue’s recent campaign to appeal to people fifty years old and over is the realization that as a person ages, their concerns change as well.
(A) the realization that as a person ages, their
(B) the realization that as people age, their
(C) to realize that when a person ages, his or her
(D) to realize that when people age, their
(E) realizing that as people age, their

Please let me know the answer ? Is C correct?

Since the campaign is referring to people, the rest of the sentence should
logically refer to people and not persons.

Also, we need to use the subjunctive mood here to indicate "proposal"
which means there should be a <that> followed by the infinitive form
of the verb.

"legacy ... is the realization" sounds better

My pick would be B

A is incorrect as the pronoun "their" does not agree with "person"

C is incorrect as it refers to a person not people

D sounds awkward. "legacy ... is to realize"

Clearly there's something to distinguish between "then" and "as"
as used in the sentence here.

Maybe someone can shed light on where to use "when" and when
to use "as". My understanding is that "when" is used to indicate
time while "as" is used to indicate similarity etc.

I choose C because of concerns
as this word is for singular nouns, the word before it should be a singular

only C does this

but i feel 'to realize that' is somewhat awkward with the whole sentence

can someone explain....

I would go with B, as it clearly defines about the people not a single person.
'C' changes it to "a person".

Amit