It won't work because 2013 will save the app as a 2013. I made that error and I had to switch everything to 2013. I don't understand why MS acts this way...
Interesting, because I can use an Access 2003 back-end on Ac2013 and it didn't try to convert it. Of course, I was starting with Ac2003 for the back end as opposed to down-converting it.