Homemade fresh garlic dressing fridge life
Really it is dependent on the acidity of the mixture. For example if you were pickling the garlic you could have a shelf life of several months. However using olive oil changes the acidity lowering the shelf life. If I remember correctly, at the last restaurant I worked at we only kept our house made vinaigrette for 7 days. 

On a side note, keeping your mixture in the fridge is extremely important in order to avoid botulism which is found in soil and on the surfaces of certain produce.