Hello, Sunnyfield, I am not in that field but in my profession only strong candidates, those on the short list, are flown in for interviewing by the top execs.
I did have a friend who got such a job after a trip like that, and he kept it for quite a while, but one reason that business always brought executives in for a final check was that the people who ran it were control freaks.
Probably not true in your case, though (this was a family held company and the family was dictatorial). He still worked for them for at least a decade, but it kind of got on his nerves over the years and he eventually left.
They know your age already; just remember that your experience will be of most relevance and value to them. If it's a social company, they will want to see if your party/dining manners are to their taste.
Interviews are stressful, but you are a top contender if they are flying you in for a close look.