Hi Jonathan, I'm from Italy so I can help you and give some advices.
- The legal age is 16 for alcohol and cigarettes and generally they don't ask you tu demonstrate that. Few markets can request, for their own politic, the age of 18 on selling alcoholic but don't be afraid, that's rare.
The little problem is that the automatic machines that sells cigarettes when markets are closed need that you demonstrate your age of 16 with a sanitary card that only italian citizens have. As consequence, remember to buy them when they're open!
- A can of beer costs from 50 cent (0,5 eur) to 1,5 eur, depends of beer. Commercial beers like Beck's or Heineken cost a little less than 1 eur, italian beers lesser. Imported beers like the belgian ones can cost more. A packet of 20 Lucky and Marlboro reds cost 4.60 euro and are the most expensive ones.
- You need specific licenses to drive, but in Sicily you can find some that leave you hire scooters (50 cilindrate) without any certification ;)
Hope have been helpful :-) Enjoy Italy!