Elder, Elderly, Older people
Often a candidate will attempt to use synonyms in order to avoid repetition, but this can lead to incorrect meaning.
I'm pretty sure that our writer in the opening example actually meant to say..
The word elder has quite specific meanings:
1. Elderly
elderly couple
In the above photo we see an elderly couple. Both man and wife are retired. They do not work. They may be beginning to experience some health problems and they may even have difficulty walking. They are probably in their late seventies or older. These people are elderly.
2. Elder(s)
meeting with village elders
In this next photo we see an army officer meeting with senior members of a village council. The council members have been chosen by the community to represent them when important decisions need to be taken about the future of the village and the welfare of the community in general. These people are elders.
3. Elder(s)
elder child
And in this final picture an older student is assisting a younger student with his reading practice. In this case the older student is the elder of the younger student. At school we often consult our elders when we need help with our homework, etc.