It is estimated that in time to come many countries will have proportionately higher number senior citizens than adults and young people combined. In my opinion, this is a negative development as higher proportion of senior citizens would put enormous pressure on health care facilities and tax revenues for such nations would considerably fall.
One of the downside of this trend is that these nations would require higher number of medical centres to tackle the needs of these people. People above the age of 60 require periodic medical attention owing to the fact that at this age their immune system becomes weak, and they are more prone to illnesses. This means that government of these national would need to set up additional facilities to meet the need of these people. For example, it is estimated that Japan government to double the number of health care facilities to meets such populations need by 2020.
Another major drawback of this shift is that this would result in lesser tax revenues for the authorities. As more and more people will turn senior citizen they will retire from their jobs and professions and start living on pension. This means that lesser percent of population would be working; as a result of this phenomenon income tax collection would decrease considerably. For example, income tax collection in UK has decreased by 3 percent in last decade as working population has decreased due to more retirements.
To recapitulate, higher percentage of aged people will not only put strain of medical facilities of a nation as they require regular care but also result in decreased tax revenue collection because of lesser working population which is not a positive development.