What's the difference between?
-"elder and eldest" are used for members inside the family.
-My elder sister- My elder brother- My elder grandson
Another limitation is that "elder and eldest" apply only to people, but "older and oldest" may refer to people and inanimate objects alike.
-my older car(✔) -my older camera(✔) -my older neighbor(✔)
-my elder car(X) -my elder camera(X) -my elder neighbor(✔)
"elder" is not followed by'than'
-He is elder than John.(X)
-He is older than John.(✔)
-Another use for "older" is that it can end a sentence.
-You can get married when you are a little older. (✔)
-You can get married when you are a little elder. (X)