A mature man can't get it up with a young woman, and so this threesome fantasy might be exactly what you're looking for. It's perfectly normal for men in their thirties to have a fetish for older women, and these are usually women who are much older than them. If your boyfriend is the sort of guy who gets turned on by younger women, he may very well turn up his nose at your suggestion of a threesome, but if he's got a real burning desire for an older woman, there's a good chance that he would love to give his partner a threesome..