Many languages have terms for siblings that define whether one is younger or older in relation to another sibling.
In the case of Peter (Simon) and Andrew, Simon was assumed to be the older of the two brothers in Navajo because he typically is mentioned first. (See Wallis 2000, p. 103f.)
In Batak Karo, the Greek term for the English term “brother” “is the term for a male having the same father and mother as the reference person, ‘brother.’ The general term for this in Batak Karo is ‘sembuyak,’ but the language prefers a particular kinship term in relation to the reference person. The Revised Standard Version translates the first part of Matt 4:18 as follows: ‘As he walked by the Sea of Galilee he saw two brothers, Simon who is called Peter and Andrew his brother.’ The first problem here is how to translate ‘two brothers.’ In Batak Karo, if translated literally it will mean that the speaker and the ‘two brothers’ are all brothers. Therefore the relationship between the ‘two’ has to be stated, that they are related to one another as brothers, which in Karo is ‘dua kaiak si sembuyak’ (literally ‘two persons who are from the same womb’). The second problem is the relationship between Simon and Andrew: which of them is older? On the basis of Semitic usage, the older is usually mentioned first (see Gen 4:8; 35:23). So Andrew is Simon’s younger brother; and therefore the translation will be ‘Petrus ras agina Andreas’ (‘Peter and his younger brother, Andrew’).” (Source: M.K. Sembiring in The Bible Translator 1992, p. 217ff.)
The Chilcotin translators tried to circumvent specifying who of the two is older, even though the language also uses age-specific terms for siblings. In Mark 1:16, they have used the generic term ˀelhcheliqi (“brother” without specifying who is older). (Source: Quindel King)
See also James / John (relative age).