OP is saying - make a law where there's a cut off limit for people having sex. Like, everyone born on or before December 31, 1979 can have sex with anyone else born on or before December 31, 1979, but they're not allowed to have sex with anyone born on or after January 1, 1980.
My hero you actually understand at least partially autistic kids
One, phrasing. Geez man.
Two, some are passed down. A mother with blood borne STDs can pass those down to her child. Also, do you really think that law would be followed?
Let's see if I can clear this up:
"If you make a law where anyone who is currently 5 years old, in the future, only has sex with someone younger than they are, and those younger don't have sex in the future with anyone currently over 5, that would get rid of all STDs."?
The man is saying that if we had a generation of children without STD's and avoided contact with those who have them, we could eradicate them almost entirely, this is a very true theory, but I don't think anything was said about it actually happening.
HIV, Syphilis, Herpes, and others can be transferred through drinking after someone, and very other small examples of trading bacteria.
Long story short, I think it's a cool concept and could work, but not only would be extremely difficult and have drawbacks, it'd be a near impossible thing to completely enforce.