JSFiddle - React, Tailwind, and code Playground

JavaScript

var items = [
    {"id":"1","age":"20", "region":"Y"},
    {"id":"2", "age":"20", "region":"X"},
    {"id":"3", "age":"31", "region":"Z"},
    {"id":"4", "age":"35", "region":"Q"}
];

var ageGroups = _.groupBy( items, "age" );

console.log( ageGroups );