Can an adult child, age 24, live with a parent in a 55 and older apartment complex?

Yes, if that particular apartment allows the second tenant to be under 55. Some do, some dont.

Yes. Age 55 or older is meant for one or more owners to be of that age and a male owner. Our community advertises that but a female only has to be 45. And, 20 percent of the residents are supposed to be under - something like 25 years old although the minimum age is 19. However, the community has no authority to enforce it. It is not a law in any state or province, nor is it a Federal law. In fact, it is against the First Amendment - It is clear discrimination. They tried it in Canada and lost the lawsuit on its merits - discrimination. In the U.S., they rely on the ignorance of the American public. "They" are not involved in the purchases of the homes anyway. Anyone can buy a home in a 55+ community.

no, if the complex is for 55 only it means no one living there can be less than 55

No it is for over 55s only.

no, 55 and older means just that

No. " 55 and older" That is easy to understand.

no. What part of 55 and over don't you'e understand?

No It would say that in the lease agreement. So ask the management and look in your written lease agreement.

You have to declare all adults who are living in the household in that apartment.