Senior is a more relative term than senior citizen. It refers to persons who have more years of experience, but who are not necessarily older in years, such as seniors in high school or senior bank officers. Golden ager tends to connote a carefree, fun-loving, older person. For some, the term suggests that older people are not to be taken seriously and their contributions to society are frivolous. Others view it as a euphemism that glosses over difficulties that can arise in later life.
Older adult is a neutral, less stereotypical terms.
Older is a relative expression, since everyone is older than someone else. The word adult connotes respect, independence, and responsibility. Variations of this term are older person and older individual . For these reasons, older adult is now the preferred term for most public speaking and expository writing.