Dear David,  

The matter of health has to be taken in context. What each order will consider 'average health' will be seen in relation to its specific spirit and apostolate, and the various practical commitments entailed in each one's way of life. Also, with the help of medication, many conditions that in the past would have ruled out religious life, or a particular kind of religious life, may no longer be a problem nowadays.  

That's a general answer. Now, to get more specific, if you have a medical condition and want to join a particular group, no matter which one it is, you need to get to know them. Once you have gotten to know them and think it may be the place, bring them information on the exact details of your condition. They will examine its nature, consult as regards the side effects of any medication you take (both long and short-term effects), obtain a prognosis to see how it may affect in the future your ability to live their life, etc. Based on what they see they should be able to come to a conclusion and give you an answer, and possibly make some recommendations if your condition rules them out, but not necessarily the priesthood.