Well not to disagree with UPT-hopeful, but it can be done with 0 face time.  The guard unit I was selected for I had never been to visit.  I am sure visiting will not hurt you by any means, but it is not always a necessity.  Make sure when you do interview/visit to be confident when talking to the people you meet.  Be respectful, but remember, they were in your shoes at one point. Not that I am some old wise man, Just my .02 on the matter.    
In answer to your?'s 
82 P 
72 N 
99 PCSM 
131.0 HRS 
 
I am only 22 so age was not a factor for me