There is no direct link between yogurt and length of life except that yogurt bacteria are very healthy for your stomach.
Your stomach contains many different kinds of bacteria if you are healthy which aid in digestion of food. One of those kinds of bacteria is a strain that is the same that makes yogurt so whenever you eat yogurt you are eating actual living bacteria.
All yogurts contain these friendly (pro-biotic) bacteria. It's what makes milk turn to yogurt. And they are good for you, particularly if you have recently taken anti-biotics which will have killed off most of your stomach bacteria. Yogurt is a very fast way to help replenish these bacteria.
But they have no proof of extending life and Dannon, the yogurt maker, was just fined millions of dollars for making false claims about the health benefits of their yogurts and ordered to change their advertising.
But yogurt is good for most all people who are not lactose intolerant so eat yogurt... it's good for your stomach and your health.