Elder is a comparative term, meaning it compares the ages of two or more individuals in a group, whereas older is a descriptive term that does not imply a comparison.
The key difference between elder and older is that elder is used to indicate a hierarchy or seniority in a family or group, while older refers only to age.
“Elder” is also used as an adjective to call a brother or sister older than a person, e. g. “He is my elder brother.” “The elderly” means a general group of people of advanced age. “Elderly” is also used as a polite adjective for “old” relatives, e. g. “He is nearly 50; he has elderly parents”.
Elder and eldest both are used for persons only and that too for family members. These cannot be used for the persons other than the family members. Eldest means the first born in the family. Elder is not used as comparative degree, so it is not followed by than.
Elder and older are both adjectives that mean "more advanced in age." Older can be used of people and things ('an older sibling;' 'an older house'), but elder can only be used of people ('the elder son'). Additionally, elder can be used as a noun ('respect your elders').
Eldest and oldest mean the same thing, but “eldest” is only used to refer to a person—almost always a member of a group of relatives (e.g., a sibling). The eldest son did not want to take over the business.
Firstly, it's the elder or older of two. It's the eldest or oldest of three or more. We use the comparative for comparing two objects and the superlative for more than two. In a sentence like this, we prefer elder and eldest for people, and use older and oldest generally for things.
Terms such as older persons, older people, older adults, older patients, older individuals, persons 65 years and older, or the older population are preferred. Use older adults, a term less likely to connote discrimination and negative stereotypes, when describing individuals 65 years old and older.
Each California County has an Adult Protective Services (APS) agency to help elder adults (60 years and older) and dependent adults (18-59 who are disabled), when these adults are unable to meet their own needs, or are victims of abuse, neglect or exploitation.