So far it looks to me that the you have started to learn pure Perl on the basis of your ability to make such a simple program. As dragonchild had pointed out, you can use arrays in place of scalars... however this still is not enough to make your code shorter as you wanted.

At this stage of your development, you should start using modules to make life easier. Your calendar program should be enough, so start moving on.

But if you insist, try downloading a CPAN module for a calendar application. Try opening the module and learn from it. Learn how the author made his implementation.