Hi Graham. One of the things I worried with our application was our age gap. The way we dealt with it was just being bang on with photos and proof of visits and skype logs etc to make sure that the ECO knew it wasnt a sham arrangement or the like.
I was also advised that the ECOs arent there or shouldnt be there to cast judgment on that score.....the only thing that bothers them is if it is a sham arrangement and a large age gap could, in their eyes, indicate that. Or so I was told.