Why is this newly created object arranged in ascending numerical order?

Question

When I run this code

var OrderPeople = function (people) {
    var byAge = {};
    people.forEach(function (person) {
        byAge[person.age] = person;
    });
    return byAge;
};

console.log(OrderPeople([ { age: 83, name: 'joel' },
{ age: 46, name: 'roger' },
{ age: 99, name: 'vinny' },
{ age: 26, name: 'don' },
{ age: 74, name: 'brendan' } ]));

I get the following output

{
    26: {age: 26, name: "don"}
    46: {age: 46, name: "roger"}
    74: {age: 74, name: "brendan"}
    83: {age: 83, name: "joel"}
    99: {age: 99, name: "vinny"}
}

I was wondering why the new object is arranged is ascending order and not just returned in the order it was before.