I can see with a 18 year history of mtb, you would be afraid of fast decents. When I mountain bike, I will probably fall or wreck an average of 5 times, though this can be linked to the fact that I usually ride the trails when they are in no so favorable conditions. I always take it slow on decents on the single track because a wreck can mean severe injury or death because of the trees everywhere.
You'll get your confidence eventually. Just ride with your fingers on the levers. I love decents but I always keep my fingers on the levers for emergencies. Pretty soon you'll find 40 great, 45 better, and 50+ amazing.