It's fashionable in some quarters to blame low fertility for situations like the aging of the Japanese population. This is almost entirely nonsense. The real problem is that too many people are living to old age. If Japan had enough people under 65 to have an over 65 population ratio like that of say, Kuwait, its total population would be nearly a billion and a half. It's simply not practical to breed ourselves to a small over 65 population ratio.
Unless you adopt policies that will kill off large numbers of oldsters - for example the Ryan budget - you have to face that fact that society will need to devote a significantly larger portion of its resources to caring for them.