Elder- only goes before a noun:
My elder sister :tick:
She is elder than me :cross:
Older- can do both:
My older sister :tick:
She is older than me :tick:
Hi Use elder - the eldest if you speak about memebers of family and other people use old- older - the oldest
She is my elder sister
This is Ithe eldest member of my family
I am older than Tom ( he is my huband)
This is the oldest woman i n the office
In comparisons between two persons, elder means "older" but not necessarily "old": My elder sister is sixteen; my younger, twelve. (Eldest is used when three or more persons are compared: He is the eldest of four brothers.) In other contexts elder does denote relatively advanced age but with the added component of respect for a person's achievement, as in an elder statesman. If age alone is to be expressed, one should use older or elderly rather than elder: A survey of older Americans; an elderly waiter.·Unlike elder and its related forms, the adjectives old, older, and oldest are applied to things as well as to persons.