Hi Bel. Older is a comparative adjective related to Old; and Elder is a person older than others. E.g. -> Lucy is older than her brother -> You must respect your elders

Elder is only used with people. Older can be used with anything. Elder is the better word to use if you are specifically talking about a persons age.

The easiest rule-of-thumb is to use older for the adjective and elder for the noun. This will work just fine 99% of the time.

Hello Bel! They are synonyms and elder sounds more formal than older. Older indicate someone or something more aged than another one. For example: David is older than me / This chair is older than that one. Elder has the same meaning of older (comparative) but you can use it only talking about human beings and mostly in family relationships; you can't add "than" like after older. For example: Lisa is my elder sister (otherwise would be: my sister Lisa is older than me). Furthermore, elder can indicate someone of higher rank, such as a corporal or a manager. In everyday speech older is widely used, rather than elder. Hope I have clarified! All the best, Noemi

It depends on the context but they likely mean the same thing. Older is much more commonly used though. Elder is usually used in the forms "an elder," "an elderly person" (an old person), or "respect your elders" (give older people the respect they deserve). Hope this helps!