Double-glazed units typically have an effective lifespan of between 10 and 25 years.
How long they last depends on many things - how ell they were made in the first place, the way they are installed, and environmental conditions.
If you're getting a draught in a room the cause is more likely to be a failed or ill-fitting frame seal, rather than the unit itself. When the units fail you'll see a faint misting inside the unit itself, indicating that the seal between the two pieces of glass has failed, and is allowing air inside. When that happens there's nothing you can do, the unit must be replaced.