Keep a good lookout
When talking about flying, always keep a good lookout. If possible, try to get an Information Service from your loved one who can keep you updated with other conversational traffic, and advise you when avoiding action is needed.
Actually, if and when the glaze appears, I don't turn-off, but ask the person if they would like to go flying sometime. This tends to produce either a very positive reaction or a very frightened or guarded one. When it gets personal for the other person, it's surprising how interested they can become. Many people just don't think it is possible that they could fly as well.
At the risk of verging off this thread, just recently, I tried this, and it turned out that the other person has a real physical fear of flying, but is fascinated at the prospect of being able to fly "where I can see what is going on". So we're going to try on friday, ever so gently.
Maybe being a bore is nothing to do with flying, but more to do with only talking about your own experiences.