use strict;
use warnings;
use DateTime;
use IO::Prompt::Tiny qw( prompt );

# Get a DateTime object for birthday and now based on user input.
my( $bday, $now )
  = map { DateTime->new( prompt_date( $_ ) ) } qw( Birth Today's );

die "Birth date must be in the past.\n" unless $bday < $now;

# Perform the math.
print "\nYou are ", $bday->delta_days($now)->in_units('days'), " days old.\n";

# Prompting: pass date entry type, receive a day=>__, month=>__, year=>__ hash.
sub prompt_date {
  print shift, " date entry:\n";
  return map { $_ => prompt "\tPlease enter $_:" } qw( day month year );
}