Focus on your relationship than the age. This is where I don't understand the constant worry about age gap when everyone says age is just a number. I never once thought/asked about if my interracial marriage to my wife will be a concern for immigration purpose, especially when it's uncommon in my wife's country. I just focused on documenting that we are a real couple.
Think of it this way, if you are worried about age then you will give the CO the same vibe at the interview and you don't want that. Work on showing them that you are in a real relationship, and keep it at that.
