My experience is that it depends on what type of memory it was. My father was Army and was in India before WWII broke out. He would often talk about pre-war India and any enjoyable experiences during the war. This included being transferred to the Middle East and finding a book shop in Cairo which sold English language books and had an excellent section on classical music. However, he would most definitely not talk about the actions he had been in.
When I was eleven years old we moved and our new next door neighbour turned out to have been a sergeant in my father's regiment. Naturally they reminisced about old times and I could, by keeping out of sight and eavesdropping, hear some of the tales. It was noticeable that when I, my sister or the sergeants’ daughters were present they both stopped reminiscing and changed the subject.
I also noticed this trait in other relatives. When I was younger it used to frustrate me that my grandfathers, uncles, aunts and parents would not talk about their experiences. There was a wealth memory that has been lost from WWI in Europe, the Middle East, Asia and Africa to post WWII in the same areas (including an Uncle on the Russian Convoys). Now I am older I think that I understand. It really is the shared experience that makes you want to talk. Sometimes the reality can only be expressed if you already know what happened.