Teenagers now engage in more virtual interaction over social media, and the number of teens with driving licenses has decreased dramatically over the same period - I think the scope of their social interaction has increased, but they have significantly less physical privacy. They spend more of their time in contexts where adult monitoring is possible. 
I also think the availability of porn and the increased pressure to adopt a low-time-preference mindset also alters the risk&#x2F;reward calculus of potentially procreative sex. With the disappearance of much well-paid blue-collar work, both in reality and the public consciousness, derailing the fast track to college is much more costly than it was in the past.
On a more speculative note, I can&#x27;t help but wonder what the effect of more widespread hormonal contraception has been on female sexual desire, and maybe even on the prevalence of environmental estrogens potentially affecting males.