I read something about this card and it implied that you receive discounts on transportation passes if you have one. What are the details about this card and are you eligible if you are 29 years old.
Here is the website.
http://www.veneziaunica.it/en/content/rolling-venice
Cost is 6 EUR to buy the card, then you get 18 EUR of the cost off 3-day transport cards, such as the 3-day vaporetto pass which is normally 40 EUR, so you get it for 22 EUR. The passes that include either a one-way or round trip on the No 5 airport bus also apply.
As far as the discounts, you'll have to click through on the website to discover what the are.