older or elder?

Yesterday a student of mine had a question for me: when saying "my older brother" or "my elder brother", which is better?

Elder is a comparative form, which means the elder of two people, especially brothers and sisters, is the one who was born first. See the following sentence:

My elder brother always finds faults with what I did.
I am the elder of the two.

However, it is more usual to say older. In such case, elder can be replaced with older.

My older brother always finds faults with what I did.
I am the older of the two.