var age = 90;
if(age > 17 && age <= 30){
alert("你已经成年了");
}else if(age > 30 && age <= 60){
alert("你已经中年了");
}else if(age > 60 && age <= 80){
alert("你已经退休了");
}else{
alert("你岁数挺大的了~~");
}