OK I will take a different approach. I think you frame is too small! I am pushing 70 and think I am the exception, but my bars are 2" lower than my saddle. I find that doing sit ups and abdominal exercise helps with the back issues. Strengthen that core and you will do better.
This is my main ride which I enjoy the most. Note that the stand kicks up the back a bit.
P1010551, on Flickr