app.js

process.stdin.resume()
process.stdin.setEncoding('utf8')

function isANumber(age){
    return !isNaN(age);
}
console.log('Hello ! What\'s your age ? ')

process.stdin.on('data', (age) => {
    if (isANumber(age) === true && age <= 99) {
        var birthYear = 2017 - age;
        console.log('You were born in ' + birthYear);
    } else {
        console.log('that\'s not a number fella...');
    }
    process.exit()
})