A recent study on the life expectancy and mortality rate of people retiring at different ages shows some correlation between continuing to work and longer life:
Researchers have disproved the theory that people who take early retirement enjoy longer lives as a result. In fact, those who stop working at 55 have nearly double the death rate of those who continue to work on until they reach 65, a study suggests.
Poorer health forcing some to retire early may be a factor, say the authors.
However, this would not entirely explain the differences they found, neither would factors such as sex and socioeconomic status.
Of interest are the effects on health and longevity not already accounted for by existing poor health forcing an early retirement. It's entirely possible that the study authors failed to account for more subtle effects of individual rates of age-related degeneration leading to a retirement decision, but it seems equally likely that "use it or lose it" effects are taking place, both physically and mentally. Stay working, and you are more likely to benefit from whatever exertions you are making in the course of your employment.
Enforced retirement ages in many countries are already quite clearly a monsterous, unethical consequence of entitlement and wealth transfer schemes - and the dangerous mindset of positive rights and enumerated freedoms underlying it all.
There is an even bigger issue here, and it concerns nothing less than the essence of liberty. It is best brought out by considering the distinction, originally due to the British philosopher Isaiah Berlin, between negative and positive freedoms. A negative freedom is a freedom from, whereas a positive freedom is a freedom to. For instance, freedom from being forced to get your neighbor ice cream is a negative freedom; freedom to get your neighbor ice cream is a positive freedom.
In the liberal-political tradition, the essence of liberty consists in an open-ended horizon of negative freedoms. Man is deemed free to do as he pleases as long as he does not infringe on the (equally valued) liberty of others. By contrast, in the socialist tradition, a man's liberty is conceived as essentially a bundle of positive freedoms. We are free to do whatever the government allows us to do. The government may make generous allowances, but unless it does, we have no freedoms we can rightfully call our own.
I don't think that we need any further utilitarian justifications for their abolishment to make the case. If you are willing to work, how is it in any way right and proper for you to be prevented from doing so by government employees?