Question
If I get old manure from the farmer next store (cow)
and want to use it on flower beds, how do I tell if it is old enough to not burn anything?  it looks old and decayed but.............................

Answer
I am not sure how you could tell if it is "old" enough.  The thing that you need to do is compost the manure.  I am attaching a website that goes through these instructions very clearly.  Depending how much you have -- meaning if there is not just tons of it -- you can choose to ignore the part about building a bin, etc., and skip to the last part of the article about the tarp and turning the pile, etc.  Let me know how it turns out so that I may do this myself one day!  Good luck.

http://gardening.wsu.edu/stewardship/compost/manure/manure1.htm

Also, be sure to not put any of this compost on vegetables, etc., that you may be eating unless you are 100 percent it is composted completely.  As an amateur "composter," I would put this on other vegetation and use either store bought compost for my food crops or traditional compost that does not have any fecal matter.
Take care,
Vikki