I'm not sure there are any risk factors. You are 76 and with age the heart muscle does start to stiffen. With the amount of exercise you have been doing over the years can determine how much this affects you. I would say not much in your case. Your EF is fantastic, which shows that plenty of blood is being pushed out of the heart to feed your body. When diastolic dysfunction is apparent, the filling of the heart is impaired, so there's less blood to be pumped out with each stroke. Yours is still performing A1. Now, it COULD be that your heart has adapted by increasing the internal volume of the ventricles, and thickening the muscle, but your echo would have detected this and reported it. So all in all, it looks to be ok to me.
If your Cardiologist believes it to be something more than age related, he/she will organise more tests. They may even want to due this as a precaution, but as I said, stiffness comes with age.
I don't think there is such a thing as a Echo that doesn't find some "mild" problem(s)... great EF !
Yes, my answer would have been: your risk factor is 100% that you are going to die. When it comes to the "when?", it gets a little fuzzy - my guess is, you'll live another 30 years.