普通にとれた
var json = {
"data" : [
{"name":"香坂健史","age":12,"gender":null,"birthday":"1971/03/30"},
]
}
console.log(typeof json.data[0].name);
console.log(typeof json.data[0].age);
console.log(typeof json.data[0].gender);
console.log(typeof json.data[0].birthday);