use warnings;
use strict;

my %age = (
    years  => 28,
    months => 0,
    weeks  => 0,
    days   => 3,
);

print 'You are ';
for (qw(years months weeks days)) {
    print "$age{$_} $_ " if $age{$_};
}
print "old.\n";

__END__

You are 28 years 3 days old.