const users = [
	{
		name: "Tayfun",
		surname: "Erbilen",
		age: 27
	},
	{
		name: "Mehmet",
		surname: "Seven",
		age: 27
	}
];

const newUsers = users.map(user => {
	user.fullName = `${user.name} ${user.surname}`;
	return {
	    fullName: user.fullName,
		age: `${user.age} years old`
	}
});

console.log(newUsers)
console.log(users)