Depending on the design of your bow and how well vursed in your tillering skills you could easly make an adult bow.  Just glue on a handle and tiller it out.  It takes very little Osage to make an adult bow.  I have one that is 52lbs 62in long an inch wide or less in spots and definitely under 3/4 thick.  I hunt with it and killed a very nice buck with it this year.  
You could always put a layer of sinew on the back for protection or some thin rawhide.  
Patrick