The advisement for replacement of the airbag itself is the only concern. It was updated a few times, I believe originally it was scheduled for a 10 year life, this i belive is noted either on the drivers door jamb, on the body side by the latch striker on a sticker label, or possibly on the inside of the gove box door. I believe the current limit for your car was changed to 15 years. The main concern isn't the explosive propellant, but the bag material itself. So at 15 years, yes you are due for a drivers airbag, but it is quite expensive.
My personal opinion is that I wouldn't replace it, just use the seat belt, which contains an ETR reel anyways, which will help, and hope for the best as far as the condition of the airbag material is concerned.