HELLP please I don't understand why that doesn't work HELP

[nate-gentry]

function basicTeenager(age){
if (age == 13-19);
{ return "You are a teenager!" }
}

function teenager(age) {
if (age == 13-19);
{ return "You are a teenager!" }
else { return "You are not a teenager" }
}

function ageChecker(age){
if (age == 13-19);
{ return "You are a teenager!" }
else if (age <= 12);
{ return "You are a kid" }
else { return "You are a grownup" }
}

function ternaryTeenager(age)
 { return age == 13-19 ? "You are a teenager" : "You are not a teenager" }

function switchAge(age)
{ switch(age) { case age >= 13 && age <= 19: return "You are a teenager" default: return "You have an age" } }