Donald Trump celebrated his 70th birthday Tuesday without much notice. This marks a sea change in American politics because the public apparently is no longer very worried about advanced age in presidential candidates. No one seems to talk about it any more.

If elected, Trump would become the oldest person to assume the presidency; he would be older than Ronald Reagan by about seven months. The presumptive Republican nominee of 2016 doesn't look very old, and he seems to have plenty of energy to do the job. So his critics aren't using his age against him. In addition, Democratic candidate Hillary Clinton is 68, so there is a virtual certainty that a senior will be in the White House in January.

It was Reagan who largely put the Age Factor to rest. He was the oldest person ever elected president, turning 70 in February 1981, less than a month after he took office.

Throughout the 1980 campaign, there had been concerns measured in polls that he was too old to do the job. But Reagan was a master delegator, not a micromanager like his predecessor Jimmy Carter, and he knew how to pace himself and conserve his energy. Reagan's image as an amazingly fit septuagenarian was enhanced when he made a remarkable recovery from an assassination attempt in 1981.

But Reagan turned in a weak performance in his first debate with former Democratic Vice President Walter Mondale, 56, during the 1984 re-election campaign, and this briefly revived the age issue. During another debate with Mondale a bit later, Reagan was asked if at 73 he was too old to perform his duties.

He replied with a joke: "I will not make age an issue of this campaign," he declared. "I am not going to exploit, for political purposes, my opponent's youth and inexperience." This got a big laugh from the audience, even from Mondale, and pretty much ended the age issue. Reagan went on to have a largely successful presidency.

A recent NBC News/Wall Street Journal poll found that 53 percent of voters are comfortable with a president over the age of 65, and only 26 percent have reservations.