I'm a very voluptous, large, self assured, attractive woman that by all medical definitions am WAY too heavy. I have curves, lots of them and NO hangups about my body, so not all larger ladies have body image issues. Good Gawd man, open your eyes to the possiblities that a real woman can offer...
Younger women are not necessarily more sexual, that seems to be another urban myth. Most of my mature girlfriends comment that they are more sexual as they have aged. But then again, perhaps like minded people are drawn to each other.
I don't know where you do your "research" but you may be looking at very skewed data...depends on the parameters set when the data was collected. Has this "data" been verified with additional data collection systems? Don't just depend on one study, look at several similar ones.