Steve: I've dove Boynton a few times and most of the reefs are more like 60 feet: a good operator is Underwater Explorers: the owner, Kevin, is a scubaboard member. You can call his boat operation and find out if I am wrong and if there are reefs closer to 50 feet. If you let him know that you are a new diver, you can probably arrange for an in-water dive guide.
A little south of Boynton is Pompano which has a lot of reefs less than 50 feet. Some of the nicest shallow reefs I've dove are at the Pompano Drop Off area and the Nursury. These are 25-30 feet reefs.
Dive Operators in Pompano include South Florida Dive Headquarters, Pompano Dive Center and Scubatyme.
I'm sure other SB'ers will chime in with their favorites as well. I've been on the above 4 boats and have had good experiences on all of them.