check to make sure the value is the number of age

function checkAge(age) {
  if (age < 19) {
    console.log('you are a kid')
  } else if (age > 18 && age < 50) {
    console.log('you are an adult')
  } else {
    console.log('you are an senior')
  } 
}

checkAge(20)
checkAge(18)
checkAge(51)