
The results are unsurprising, but interesting. The New York Times has a summary.[2]
[1] https://www.amazon.com/Sex-America-Edward-Laumann/dp/0446671... [2] http://www.nytimes.com/1994/10/07/us/sex-in-america-faithful...
For one, American life delays are heavily attributable to economic uncertainty about basic needs like healthcare, whereas Japan has a healthy social safety net (related to your point about income equality and tax structure).
Effective fertility rate in particular is also radically different. As the author of the OP article points out, Japanese youth are delaying relationships and sex. In America, however, as in most other industrialized countries, the declining birthrate is mostly attributable to birth control, not abstinence.
