def underage?(birthday)
  18.years.ago < birthday
end

public static class Snippets
{
    public static int CalculateAge(DateTime birthdate)
    {
        // get the difference in years
        int years = DateTime.Now.Year - birthdate.Year;
        // subtract another year if we're before the
        // birth day in the current year
        if (DateTime.Now.Month < birthdate.Month || (DateTime.Now.Month == birthdate.Month && DateTime.Now.Day < birthdate.Day))
            years--;

        return years;
    }
}

<?php

  //calculate years of age (input string: YYYY-MM-DD)
  function birthday ($birthday){
    list($year,$month,$day) = explode("-",$birthday);
    $year_diff  = date("Y") - $year;
    $month_diff = date("m") - $month;
    $day_diff   = date("d") - $day;
    if ($day_diff < 0 || $month_diff < 0)
      $year_diff--;
    return $year_diff;
  }

?>

// ---------------------------------------------------------------------------|
// qryHowOld                                                                  |
// Description: How old someone is in the format:                             |
// XXX Years XX Months X Weeks X Days                                         |
// Birth Date could be specified like Date.UTC(2002,8,16,17,42,0)             |
//                                                                            |
// Arguments:                                                                 |
//    varAsOfDate: as of date                                                 |
//    varBirthDate: birth date                                                |
//                                                                            |
function qryHowOld(varAsOfDate, varBirthDate)
   {
   var dtAsOfDate;
   var dtBirth;
   var dtAnniversary;
   var intSpan;
   var intYears;
   var intMonths;
   var intWeeks;
   var intDays;
   var intHours;
   var intMinutes;
   var intSeconds;
   var strHowOld;

   // get born date
   dtBirth = new Date(varBirthDate);
   
   // get as of date
   dtAsOfDate = new Date(varAsOfDate);

   // if as of date is on or after born date
   if ( dtAsOfDate >= dtBirth )
      {

      // get time span between as of time and birth time
      intSpan = ( dtAsOfDate.getUTCHours() * 3600000 +
                  dtAsOfDate.getUTCMinutes() * 60000 +
                  dtAsOfDate.getUTCSeconds() * 1000    ) -
                ( dtBirth.getUTCHours() * 3600000 +
                  dtBirth.getUTCMinutes() * 60000 +
                  dtBirth.getUTCSeconds() * 1000       )

      // start at as of date and look backwards for anniversary 

      // if as of day (date) is after birth day (date) or
      //    as of day (date) is birth day (date) and
      //    as of time is on or after birth time
      if ( dtAsOfDate.getUTCDate() > dtBirth.getUTCDate() ||
           ( dtAsOfDate.getUTCDate() == dtBirth.getUTCDate() && intSpan >= 0 ) )
         {

         // most recent day (date) anniversary is in as of month
         dtAnniversary = 
            new Date( Date.UTC( dtAsOfDate.getUTCFullYear(),
                                dtAsOfDate.getUTCMonth(),
                                dtBirth.getUTCDate(),
                                dtBirth.getUTCHours(),
                                dtBirth.getUTCMinutes(),
                                dtBirth.getUTCSeconds() ) );

         }

      // if as of day (date) is before birth day (date) or
      //    as of day (date) is birth day (date) and
      //    as of time is before birth time
      else
         {

         // most recent day (date) anniversary is in month before as of month
         dtAnniversary = 
            new Date( Date.UTC( dtAsOfDate.getUTCFullYear(),
                                dtAsOfDate.getUTCMonth() - 1,
                                dtBirth.getUTCDate(),
                                dtBirth.getUTCHours(),
                                dtBirth.getUTCMinutes(),
                                dtBirth.getUTCSeconds() ) );

         // get previous month
         intMonths = dtAsOfDate.getUTCMonth() - 1;
         if ( intMonths == -1 )
            intMonths = 11;

         // while month is not what it is supposed to be (it will be higher)
         while ( dtAnniversary.getUTCMonth() != intMonths )

            // move back one day
            dtAnniversary.setUTCDate( dtAnniversary.getUTCDate() - 1 );

         }

      // if anniversary month is on or after birth month
      if ( dtAnniversary.getUTCMonth() >= dtBirth.getUTCMonth() )
         {

         // months elapsed is anniversary month - birth month
         intMonths = dtAnniversary.getUTCMonth() - dtBirth.getUTCMonth();

         // years elapsed is anniversary year - birth year
         intYears = dtAnniversary.getUTCFullYear() - dtBirth.getUTCFullYear();

         }

      // if birth month is after anniversary month
      else
         {

         // months elapsed is months left in birth year + anniversary month
         intMonths = (11 - dtBirth.getUTCMonth()) + dtAnniversary.getUTCMonth() + 1;

         // years elapsed is year before anniversary year - birth year
         intYears = (dtAnniversary.getUTCFullYear() - 1) - dtBirth.getUTCFullYear();

         }

      // to calculate weeks, days, hours, minutes and seconds
      // we can take the difference from anniversary date and as of date

      // get time span between two dates in milliseconds
      intSpan = dtAsOfDate - dtAnniversary;

      // get number of weeks
      intWeeks = Math.floor(intSpan / 604800000);

      // subtract weeks from time span
      intSpan = intSpan - (intWeeks * 604800000);
      
      // get number of days
      intDays = Math.floor(intSpan / 86400000);

      // subtract days from time span
      intSpan = intSpan - (intDays * 86400000);

      // get number of hours
      intHours = Math.floor(intSpan / 3600000);
    
      // subtract hours from time span
      intSpan = intSpan - (intHours * 3600000);

      // get number of minutes
      intMinutes = Math.floor(intSpan / 60000);

      // subtract minutes from time span
      intSpan = intSpan - (intMinutes * 60000);

      // get number of seconds
      intSeconds = Math.floor(intSpan / 1000);

      // create output string     
      if ( intYears > 0 )
         if ( intYears > 1 )
            strHowOld = intYears.toString() + ' Years';
         else
            strHowOld = intYears.toString() + ' Year';
      else
         strHowOld = '';

      if ( intMonths > 0 )
         if ( intMonths > 1 )
            strHowOld = strHowOld + ' ' + intMonths.toString() + ' Months';
         else
            strHowOld = strHowOld + ' ' + intMonths.toString() + ' Month';
           
      if ( intWeeks > 0 )
         if ( intWeeks > 1 )
            strHowOld = strHowOld + ' ' + intWeeks.toString() + ' Weeks';
         else
            strHowOld = strHowOld + ' ' + intWeeks.toString() + ' Week';

      if ( intDays > 0 )
         if ( intDays > 1 )
            strHowOld = strHowOld + ' ' + intDays.toString() + ' Days';
         else
            strHowOld = strHowOld + ' ' + intDays.toString() + ' Day';

      if ( intHours > 0 )
         if ( intHours > 1 )
            strHowOld = strHowOld + ' ' + intHours.toString() + ' Hours';
         else
            strHowOld = strHowOld + ' ' + intHours.toString() + ' Hour';
 
      if ( intMinutes > 0 )
         if ( intMinutes > 1 )
            strHowOld = strHowOld + ' ' + intMinutes.toString() + ' Minutes';
         else
            strHowOld = strHowOld + ' ' + intMinutes.toString() + ' Minute';

      if ( intSeconds > 0 )
         if ( intSeconds > 1 )
            strHowOld = strHowOld + ' ' + intSeconds.toString() + ' Seconds';
         else
            strHowOld = strHowOld + ' ' + intSeconds.toString() + ' Second';

      }
   else
      strHowOld = 'Not Born Yet'

   // return string representation
   return strHowOld
   }   
//                                                                            |
// qryHowOld                                                                  |
// ---------------------------------------------------------------------------|