Generate random birthyear

date = new Date();
year_current = date.getFullYear(); // get current year
year_min = 1900;                   // generate years starting year_min
age_min = 18;                      // generate years that guarantee you are age_min years old
parseInt(Math.random() * (year_current - year_min - age_min) + year_min);

// <TEST>
birthyears = [];
for (i=0; i < 10000; i++) {
    birthyears.push(parseInt(Math.random() * (year_current - year_min - age_min) + year_min));
}

console.log(Math.max.apply(null, birthyears)); // most recent birth years while testing
// </TEST>