firebase for Web how get data in unique key(push())

I have no idea how do I get the data("age") in unique key(generated by push()) here is my code

var dbRef = firebase.database().ref('test');
    var a = dbRef.push().set({name: "apple", age: "12", sex: "male"});

    dbRef.on('value', snap => {
        console.log(snap.val()); //I want to get age: "12" !! 
    });

here is the output(from console)

Object { -Kfq7woK-DmUsZ728lgF: Object }

please help me!