I replaced my last one when the padding started shedding on me when it got wet and I ended up with black lines on my forehead after every ride. I think it was less than 5 years old. I was given one to replace it and rode with that a few years and then bought one I liked much better, so the gift one got light mounts permanently attached for night riding. None of that means anything to you, but, if you've been riding it enough over the last 10 years for it to get manky, replace it. If you don't trust it, replace it. If you want validation that you don't have to replace it, well, if you bought it new those 10 years ago and has been sitting on a shelf out of direct sunlight, it's probably ok unless it crumbles in your hands when you pick it up. But, if there's any way you think you might not be 100% sure it's safe and think that little bit of doubt is going to be an excuse to keep you from going out on a ride, replace it.