What does it mean when you have trouble remembering certain words?

Well in my case it is age and lack of practise. I live in a country where I rarely meet anyone who speaks English and certainly no one with an extensive vocabulary. When I lived in England it still used to happen occasionally but I put it down to the fact that I was thinking ahead of what I was saying, it happens to many people and they end up not just using simpler words, but changing the intent of what they were saying.