The following code was shamelessly copied from Date::Calc's documentation:

  use Date::Calc qw( Decode_Date_EU Today leap_year Delta_Days );
  $date = <STDIN>; # get birthday
  ($year1,$month1,$day1) = Decode_Date_EU($date);
  ($year2,$month2,$day2) = Today();
  if (($day1 == 29) && ($month1 == 2) && !leap_year($year2))
      { $day1--; }
  if ( (($year2 - $year1) >  18) ||
     ( (($year2 - $year1) == 18) &&
     (Delta_Days($year2,$month1,$day1, $year2,$month2,$day2) >= 0) ) )
  {
      print "Ok - you are over 18.\n";
  }
  else
  {
      print "Sorry - you aren't 18 yet!\n";
  }
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     use integer;  # speeds up the math
     my @date = localtime(time);
       # convert year to months and add current number of months
     my $yearnow = ((($date[5] + 1900) * 12) + ($date[4] + 1));
     print "Enter an 8 digit birthdate.  eg: 01/01/1970\n";
     my ($monththen, $daythen, $yearthen)  = split /\//, <STDIN>;
       # we'll fly without error-checking now and just add what they e
+ntered for month
     my $modyearthen = (($yearthen * 12) + ($monththen));
       # subtract the totals and divide by 12, convert to int (redunda
+nt for safety sake)
       # and voila actual number of years alive
     $numyears = int (($yearnow - $modyearthen)/12);
     print "You've been around $numyears years!\n";
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use integer;

#...code ommited; obtain $days from FROM_DAYS()
#                 and $birth_year from database

my $this_year;
my @time;
my $raw_years;
my $num_leaps;
my $int_years;
my $float_years;

@time = localtime(time);
$this_year = $time[5] + 1900;
$raw_years = $this_year - $birth_year;
$num_leaps = $raw_years / 4;
$days += $num_leaps;

$int_years = $days / 365;

no integer;

$float_years = $days / 365;

if ($int_years == $float_years) {
   print "Today's your birthday!";
}

#...Then do whatever else you're going to do
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If you want to be slightly more accurate (not that this matters for another 100 years, but hey!) the leap year formula is that a leap year is divisable by 4, but not 100 (except if divisable by 400). Of course, the amount of error induced by leap years wouldn't effect your program unless the person was over a thousand years old (one day of error every four years would take a long time to become relevant), otherwise its safe to just div by 365.

Article about leap years.

I'm not sure how clear I was in the previous post. I was rather tired and stuff. The original question was:

I need to calculate someone's age based on their birthday. The birthday is being pulled from MySQL so I have the FROM_DAYS() function which will give me the number of days they have been alive. I cannot just divide by 365 because of leap years and all. Any advice on accurately calculating someone's age?

So I was trying to say that leap years are irrelevant. You have the birth date. So you just divide the number of days by 365. This will be off by one day every four years, meaning that their birthday will appear to creep at the rate of 6 hours a year. This shouldn't be a big deal though... it just means that their birthday will move forward a day every four years. This means that if a person enters a birth date for an age verification system, it would let them by 4 days before their 18th birthday or 5 days before their 21st. In almost any other application, the error is negligable.

Take a look at Date::Calc and Date::Manip.

I was just looking for the number of years alive. So like when their birthday rolls around I can say happy birthday your 10 years old. Or hey everyone John Doe is 10 years old today.

Date::Calc (or, heaven forbid, Date::Manip) is probably overkill since you only want age in years. All you really want to know is whether the birthday has passed this year.

sub age {
    # Assuming $birth_month is 0..11
    my ($birth_day, $birth_month, $birth_year) = @_;

    my ($day, $month, $year) = (localtime)[3..5];
    $year += 1900;

    my $age = $year - $birth_year;
    $age-- unless sprintf("%02d%02d", $month, $day)
               >= sprintf("%02d%02d", $birth_month, $birth_day);
    return $age;
}
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Of course, if you're only using this on a person's birthday, all you need to do is subtract their birth year from the current year :-)

Sholdn't the

if ($year % 4) {$nod=$nod-365} else {$nod=$nod-366}; #check for the le
+ap year.
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be

if ((($year % 4 == 0) && ($year % 100 != 0)) || ($year % 400) == 0) {$
+nod=$nod-365} else {$nod=$nod-366}; #check for the leap year.
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To handle Y2K (and others) correct... /t0mas

Sorry - It should be

if ((($year % 4 == 0) && ($year % 100 != 0)) || ($year % 400) == 0) {$
+nod=$nod-366} else {$nod=$nod-365}; #check for the leap year.
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365 and 366 swiched places....