The lifespan of your extensions depend on wear and tear, lifestyle, natural lashes, skin type, etc. All of these factors will affect how quickly you shed your natural lashes and the extensions.
The main factor in how long your lashes last is the glue used to apply your lashes. The stronger the glue, the stronger the bond, and the longer your extensions will last. The downside to strong glues is an increased chance of adverse reactions. The stronger glues have vapours that may cause severe tearing, itching, stinging, swelling of the eyes, and allergic reactions.