My shepsky had same issue...running up fast was ok, but coming down he would go “accelerando”...(in music, it means to go gradually faster and faster!) Then he would slip at the bottom, legs flailing, and crash into the wall!
I taught him to go down slowly by walking beside or a little ahead of him, I held my hand down in front of him saying “slowwww slowww”. When we both made it to the bottom he saw that it was much more pleasant to go down in a controlled way! He learned in several repetitions, it did not take much. When he forgot, if I Saw him coming down but I wasn’t on the stAirs with him, verbally saying “slowww sloww” worked as a reminder. Now he steps daintily off that bottom step and looks pleased with himself.
We adopted a “middle-aged” adult too ... I feel like this age is great. :-)
Rumo ~ rescue shepherd/husky mix