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.) The same choice was made in Biangai (source: Larson 1998, p. 40).
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).