Could I immigrate to Italy from Australia ?

You don't need to be an Italian citizen to move and live in Italy. If I were you I'll rather go there for a few months to study Italian (maybe getting a "working holiday" visa will help), and then decide whether you like the place enough to aim for a longer stay.

If you find a job during your working holiday, and your employer likes you enough to do all the paperwork required (without which you can't obtain a regular visa) then you're in for the long haul, and after a certain number of years you can apply for citizenship.

Why would you even want to? No offense, but why would anyone want to trade brand new and vibrant Oz for anywhere in old and overated europe?... and especially a southern country, where things like kinship based corruption are quite the blast lol. Don't get me wrong, but Italy is nothing but a museum, and an expensive one too, like the most of Europe right now actually! It has got beautiful places, but museum like.. all of them! And mind I personally love museums, but once you're done visiting the museum what else are you going to do?!

Sorry, just doesn't seem like a very good trade. You don't live in Italy dude, you just visit it!!

.........EDIT.........

Your grandparents did the smart thing, and you should actually be thankful to them every single day of your life, for having given you the opportunity to be a new world specimen!! Europe is over dude.. both as in overated and as in OVER! If you do manage to live in Italy some day you'll understand what I'm talking about... and you'll also understand why your grandparents left in the first place!

Paradox : legal immigration is difficult, while if you're clandestine sooner or later you'll be regularized.

I think it's not easy to find a job in Monza so take informations before leaving. But Monza has a bad climate, compared to Australia : cold and snowy in winter, hot and humid in summer... Are you sure it's worth ?

When seeking citizenship by descent one must have a continuous family line, such as ? If your grand parents are still italians then your parents would need to be italian as well. Then you would be italian.

Do you know if your parents are italians also ? Have your grand parents forfeited their citizenship coming to Australia ?

Ask your family.

Why?

A great place to visit, but Italy over Australia to live, why?

Yes. Google "Jure Sanguinis Italian Citizenship"

and be aware, you have permanent rights to your Italian citizenship.

Go for it if you want.