Elder mean people who are older than one *my elder brother Older having lived for a long time no longer young *my sister is older than me.

As adjectives, they mean practically the same thing. However, "elder" as a noun can be used as a polite way of referring to someone who is older than you.

I am older than you.... Show him some respect; he is your elder.

Broadly speaking, these two words have the same meanings and can be used interchangeably in most settings. Elder adds a level of respect that older does not. Elder also cannot be used when referring to animals or objects. Older is the better word choice in most situations. It’s used simply to refer to people or things far advanced in years of life. See more information here: http://writingexplained.org/elder-vs-older-difference