It's an interesting fantasy to paint such a fat ass green! Ladies with such an ass are especially good in the crawl position, a boner is assured. Except you have to have a decent length tool. If you don't have one, I recommend laying the lady on her back and fucking her with your hands on her thighs pressed up against her belly. Otherwise you can't get the dick in deep.
For a mature lady, the very fact that she is given in her mouth and cum in the same place is like a balm to her body. She feels that she hasn't lost her attractiveness and competes with her younger girlfriends on an equal footing. And the attention of the males tickles her vagina so much.
I could do it too.