At age 78, Sanders is the oldest among the crowded field of Democratic candidates vying to run for president in 2020. One of his main rivals is Joe Biden, the former vice president, who at 76 is not much younger.
Indeed, Biden's floundering speeches and patchy memory on the campaign stumps have also raised questions about whether his health makes him fit for office.
Given that a US president is said to be the most powerful man in the world, there is no doubt that the job comes with massive pressures severely testing mind and body. If Sanders or Biden were elected in 2020, both would be in well in their 80s by the end of their office tenure.
It makes you wonder, therefore, if there should not be age limits set for potential White House occupants. The responsibility of the job is immense, not least from having the authority for deploying nuclear weapons under possibly nerve-wrecking conditions. Shouldn't the president be someone of full health, both physically and mentally?
The public performances of Sanders and Biden are hardly inspiring. Before being taken into hospital for heart surgery this week, Sanders had to cancel a campaign event last month due to some other health issue.
Joe Biden's rambling and sometimes incoherent responses during televised debates have caused acute embarrassment over criticisms that the veteran politician seems to be showing signs of senility.
Their defenders rebuff such scrutiny, saying that focusing on a candidate's age is harbouring an unfair prejudice of "ageism".
However, it seems illogical to permit persons of biological senescence to compete for one of the most onerous offices in the world. Take other professions, for example. Would applications for airline pilots or brain surgeons not be restricted owing to age and inevitable health conditions? Why shouldn’t normal retirement age be applicable to politicians?
Admittedly, it is not an exact science. People in their 70s can appear to function with youthful vigour and mental dexterity. Democratic contender Elizabeth Warren is age 70 and seems to be full of beans.
US President Donald Trump is now 73, three years after being elected to the White House. He seems as feisty and indefatigable as ever. His mangling of grammar is arguably consistent with his combative nature over many years, and not related to ageing.
By comparison, Russian President Vladimir Putin and Chinese counterpart Xi Jinping are both 66. Both are in full health. Putin competes in judo and ice hockey. The two leaders show razor-sharp mental acuity.
Another question is why are the top Democratic presidential candidates so relatively older? In Biden's case, it seems his ambitions are motivated by vain fantasies of attaining the presidency. Surely Joe should just pack it in and let a younger Democrat like Tulsi Gabbard have a crack at it. His party handlers probably don't want to see anti-war, social justice activist Gabbard being given a chance.
Sanders, on the other hand, seems more committed personally to a political vision of transforming American society. He calls himself a socialist and wants to bring in Medicare for all, decent-paying jobs and narrowing the obscene rich-poor gap in the US. We can understand how such noble motivations would keep a person going, despite their age.
Bernie Sanders has also said several times that what America needs is a popular mobilisation around achieving a socialist program for government. Apparently, his campaign is raising more money from voters than his other rivals, and most of the donations are coming from working-class Americans. That may suggest that the grass-roots movement Sanders is calling for to transform US politics is growing.
Bernie has "name recognition" and a certain charisma. If he were to hand over the mantle to a younger candidate of similar politics, such as Gabbard, the gamble is that there may not be sufficient momentum to win the White House. Maybe it’s just a simple case that there is no-one to replace Sanders. His socialism is a one-man-band.
But the thing is there’s still a long, frenetic year to go before the presidential elections next November. Will Sanders or Biden be up for sustaining the gruelling schedule of electioneering. Will they last the course?
The uncertainty could be solved by putting a sensible age limit on presidential applicants.
The views and opinions expressed in the article do not necessarily reflect those of Sputnik.