Sergeant syther
there is no age limit you just have to be over 18. and medical problems may keep you from joining depending on how bad it is.
There is a age limit for certain ones.
42 is the age limit for active
You can reinlist if you're a veteran also. It all depends on the person.
You have to be 17 and at least a junior in high school to join.
The wrists thing may or may not be a problem they'll tell you if you are able. I don't think there will to much of a problem he just needs to get them checked by a doctor.