Japan has been suffering from low inflation and at times deflation. This means that debts do not shrink with inflation. I think the stockmarket and property markets have been pretty flat too over the period. What growth there has been has been assisted by "extraordinary" (well they were before 2008) monetary measures and growth in government debt to 230% of GDP.
Japan's working age population peaked in the 80s https://en.m.wikipedia.org/wiki/Aging_of_Japan so I don't know why anyone should expect robust aggregate growth, considering that it has been a maturely developed economy for decades.
> There are both cultural and economic barriers. In Japanese tradition, marriage was more about duty than romantic love. Arranged marriages were the norm well into the 1970s, and even into the 1990s most marriages were facilitated by "go-betweens," often the grooms' bosses. Left to their own devices, Japanese men aren't sure how to find wives — and many are shying away from the hunt, because they simply can't afford it. Wages have stagnated since the 1990s, while housing prices have shot up. A young Japanese man has good reason to believe that his standard of living would drop immensely if he had to house and support a wife and children — especially considering that his wife likely wouldn't be working.
Japan has had deflation so even a stagnating wage translates into a rising standard of living. That said, Japan has a generational gap whereby the younger people face worse challenges, but that is different from what is typically understood as income inequalities.
From 1990 to 2013 Japan's per capita income actually doubled, translating into over 3% growth per annum.