[Nyororin]

I don't know how old you are, but chances are your age will have little to do with the subject of conversation. Unless, well, you leave all the topics completely to the other person.
Conversations are a two party event, so talk about what you enjoy and are interested in. Your expressions of interest are going to be a lot more important than your age in what is talked about. The other big key is going to be the person you are talking to. Regardless of your age, if they don't know anything about what you are interested in, it will not come up.

As for your job - the Japanese military is the defense force. The majority of people will not harbor any feelings in either direction about your position. Your gender also will not make a difference. Contrary to popular rumors, Japan is NOT that sexist.