But then in 2024 Trump will be too old.
He will be barely a year older than Biden is now (might be a bit under a year, you can do the math.)
Anyone besides me remember that many people thought Ronald Reagan was too old? Taking office a couple weeks before his 70th birthday.
Just thinking ahead: given that Donald Trump is such a divisive figure I would assume the Republicans wouldn't want to touch him again. So supposing he decides to run as an independent in 2024, would the Republicans take fright, given that he has such a strong and loyal base, and realise they have no choice but to get him to run for them again, rather than split the right wing vote?
He could do that. Look at what George Wallace did to Hubert Humphrey in 1968 and Ross Perot did to George H. W. Bush.
An independent candidate will almost certainly cause the party closest to him/her on the political spectrum to lose. Almost as important as votes, independent candidates take a lot of money away from the regular party candidate. Many people say Ralph Nader cost Al Gore the 2000 election by taking over 97,000 votes in Florida in a 3rd party effort.
Personally I see the Republican Party in Congress trending toward accepting defeat. I don't see many Republican state governors arguing against the vote vigorously. I could be wrong, the noise level is so high now finding something like that is very hard.
I do see people like Ted Cruz trying to position himself as Trump's successor within the Republican Party (personal opinion)
In 2024, Trump could try to hijack the Republican Party voters again in the Primaries, thus leaving the party leadership no choice but to support him. But a 3rd party, no way it can do anything but hurt the Republicans, probably across the board into down ballot races.
EDIT - and don't worry. We will have plenty to debate/ argue about the next four years, no matter who is US President.