The best way to help others feel comfortable with your choice is to feel comfortable about it yourselves. However, you need to know that many people will feel ill at ease no matter how at ease you are and no matter what you say or do. The people who will give you flack are the ones who aren't comfortable with their own incestuous urges.
Let me explain. When an older woman hooks up with a young man, people think, 'She could be his mother!' It is normal for all of us to have sexual feelings for family members. However, most people are terrified to admit these feelings. They bury the feelings, and reject anybody whose behavior threatens to awaken such feelings inside themselves. Your relationship will awaken incestuous feelings in others.
The people who are comfortable with their incestuous urges, will be cool with your relationship. The people who are terrified by such feelings, will attack and reject you, in order to push away the threat. You have no way of helping people to deal with reactions that stem from parts of their psyche of which they aren't themselves aware.
So, basically, I am telling you that there is little that you can do to ease other people's reactions. If they can't handle their incestuous urges, they will reject you and your relationship in order to reject the temptation inside themselves, plain and simple. The bottom line is that you both need to be comfortable with your choice and let the chips fall where they may. Don't worry about trying to push the river (other peoples' reactions).
The river is going to flow with or without you. All you can do is paddle in your own boat, and, above all, enjoy your ride!