If you draw back the bow and can anchor your kisser button at the corner of your mouth comfortably, then draw length may not be your only problem. Your stance can also affect how close your string comes to your forearm. I personally shoot with an oblique stance, where I put my arrow and the target at about a 30°-45° angle to my shoulders. I have been shooting the same draw length my whole life, but those first couple trips to the range will find you needing to correct your form. If I don't have proper form, I'll hit my arm every time.
Take a look at the following site which shows the different stance types, and try shooting with an oblique stance. This may correct your problem. If you still hitting your arm, then your draw length is definitely too long.
http://library.thinkquest.org/27344/propertech.htm
Do some more searches on proper bow stance for a better explanation. This is often a very important thing that most people overlook, and assume its only your draw length that needs adjusted.
Good luck getting your arm healed and on the path to recovery.
Don