That is for employment/workers, not housing. Under equal opertunity employment you cannot discriminate agianst someone 40 or over.

For fair housing, you must not discriminate, such as refuse familys with minor children, except in a number of cases,

one being if 80% of the dwellings units must have at least one occupant who is 55 years of age or older and the community is made and operates as a 55+ place.