1) The share of the population over the age of 80 recently surpassed 10% in Japan. Japan is basically on the bleeding edge of population dynamics, and we can expect to see the same demographic changes coming to the US, China, and most of Europe fairly soon. India and parts of Southeast Asian are an exception (at the moment). It remains to be seen if they can take advantage of their young workforce by educating them properly and making sure opportunities are available.
2) Millenials in the US are the largest generation by population ever, and are having the fewest children of any generation ever. As they age, they will represent a growing plurality of the society.
3) This current trend of "we have too many old people in government" is really code for "the people in government don't represent my views", which is largely a generational opinion. As millenials age into the system, the government will start to more closely reflect their world views. So less and less will be done over time to "correct" this perceived defect in government.
4) Medical research and government policy remains focused on extending life, and less so on improving the quality of existing life. People will live longer and spend a longer period time in a deteriorated state, kept alive by medical "advances" and government policy that encourages extending life over all else. More and more money will be needed to take care of people in these advanced states, draining resources from the rest of the society. It's already happening - see the Social Security and Medicare debacle in America.
Not the most organized set of thoughts but I really think the decline in population growth (and eventual plateau at the end of the century) is going to have widespread impacts across all of society. Strangely enough, the representation in American government today is ahead of its time in that it is probably representative (age-wise) of what the population will actually look like in 100 years.