In English, we can simply say "brother"; there's not need to specify birth order all the time. If desired, we can say "younger brother" or "little brother" (but not "small" brother, as that would refer to size, not birth order). Your younger / little brother could refer to you as his "older brother" (or "elder brother" in old-fashioned usage) or "big brother". Note that, in English, brothers and sisters usually call each other by their names, regardless of birth order.

My younger brother is more common when we are talking about the 3rd person.