Also, if you think the logic isn't strong enough on its own, here are statistics from the CDC:
Young people (age 15-24) have FOUR TIMES the rate of chlamydia and gonorrhea than the general population. Syphillis, however, is more likely in adults age 20-44.
The CDC also recommends testing all sexually active women <26 for chlamydia, every year.
I'm no expert, but I think the STDs to be most concerned with those are those which are least treatable. Wikipedia says the ones you cite are bacterial, so I presume, completely destroyed by antibiotics.
So, viruses like HIV and herpes? And maybe HPV?
(still, perhaps the treatable STDs have already done some lasting damage by the time they're detected, anti-bacterials may be harmful, and it's still gross, so use condoms)
Why don’t men go for younger women? That’s not quite accurate, because they do, but we seem to have a cultural norm against girls who have recently exited puberty, even though they are highly fertile. Some time in the last few hundred years, we reached a cultural norm that as a man gets older, it’s increasingly less appropriate for him to be with a sixteen year old. That’s not long enough to override thousands of years of evolution, so what could have contributed to it?
The best solution I’ve heard started by looking at who benefits from this norm [older women] and wondering whether they could have contributed to it. After all, the strength of this norm has been increased in the last sixty years or so, which coincides with the period in which women’s power has increased.
One alternative I heard recently is that it doesn’t make sense biologically to go for women who are recently post-pubescent, as they don’t make the best mothers. Instead, a slightly older woman [mid-twenties] makes sense to be the best mother. This is perfectly plausible.
Another, less plausible, suggestion I’ve heard is that it’s to do with mental capacity. I find this unconvincing because we have few objections to a high-status man dating a beautiful but low-intellect woman.
Thoughts?