All systems have a failure rate, airbags included, regardless of age. The greatest failure probability I have read about on airbags, new or old, is failure to deploy or to deploy adequately. There are occurances of the bag deploying when not wanted.
This is part of the arguments that occured in engineering circles in the early 70s - what was an acceptable failure rate. the other arguments were "how do you limit the explosive noise from the airbag to levels below hearing damage thresholds", "How long do you certify them to meet your failure rate criterea", "What do you do with the hazardous waste from deployed air bags" "What hazard do these pose to auto dismantlers, children playing in abandoned cars, etc." "What about short people, people with glasses, children, etc", "What happens when people rely on the bag and stop wearing seatbelts"?
I always rely on my seat belt and pretend the air bag isn't even there. I am leaning towards installing a 5 point belt system instead of the airbag after it expires, if California's extreme "Papa knows best" laws allow me to do such a modification.
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E