Japan’s sexual apathy is endangering the global economy (2013) (washingtonpost.com)

"People in Japan tend to live a long time; elderly Japanese are expensive to care for because they spend so many years in retirement and because they're accustomed to a high standard of living and medical care. For any economy to stay healthy, there need to be enough taxpayers to support all the retirees. But Japan's population is shrinking and aging simultaneously, which means that the number of old people is skyrocketing just as the base of taxpayers shrinks."

Why not just set the retirement age up to mitigate that problem?

This is a case where policy will have to lead public opinion and culture. It has been done successfully in many countries, though less traditional than Japan to begin with. Subsidise childcare, make maternity leave longer, ear mark some leave for fathers etc. Then you'll see change eventually.

One solution is for Japan to start encouraging immigration. Maybe setup an H1-B program. This will increase the number of tax payers, while also increasing exports.

I'd argue that Japan's policy on immigration is just as much an issue, and easier to resolve than convincing people to have children.