What are some coditions that can keep you out of the military?

Answer 1

search for the army reg & enjoy a very long read. Pretty much the same standards (give or take a bit) for each of the services.

Answer 2

There's over 200 physical conditions which can disqualify you. I've put a link to the Standards of Medical Fitness below. Read Chapter 2 if you have the time. At present, only about 15% of adult males between 18 and 26 can meet the physical, mental and moral standards for enlistment.

Answer 3

you gotta be like almost blind or have acute asthma, mental problems like suicidal thoughts, etcetc
check out the document the person above wrote