I'm surprised at your entire post, except for the detail that Mr. Trump "plays golf", which I'm sure is a true detail.

For more information, I looked at The Lancet, which I believe is a respected medical journal. It has a very lengthy article, not about the fitness of Trump or Biden themselves, but about the effects the presidential administrations have on the nation's health. (Mainly it focuses on the Trump administration's effects.) Here it is: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)32545-9/fulltext#seccestitle300
(This link, when clicked, doesn't work directly for me but if I paste it (the whole thing, including the number 300 at the end) into a new window then it works.)

Here's the identifying information for the Lancet article, so it can be looked up independently:

"
THE LANCET COMMISSIONS| VOLUME 397, ISSUE 10275, P705-753, FEBRUARY 20, 2021
PDF [2 MB]

Public policy and health in the Trump era

Published:February 10, 2021DOI:https://doi.org/10.1016/S0140-6736(20)32545-9
"

For a comparison between the fitness of one president and another president, I finally settled on The Atlantic, a magazine that seems more assuredly respectable, and possibly less biased, or possibly less political, than the myriad of other sources that came up in my online search. (I didn't rely on the NY Times, for example, because I was sure that a lot of you here would call it politically biased.). Here's the article I found in The Atlantic: https://www.theatlantic.com/ideas/archive/2020/03/what-should-we-know-about-the-presidents-health/608392/

The article says a little about Mr. Biden and Mr. Trump, but it's about many presidents, not just them.

Here's the identifying information for The Atlantic article, so it can be looked up independently:
"IDEAS
What Should We Know About the President’s Health?
Pundits and campaign operatives dissecting years of medical records would be only more fodder for political theater.
MARCH 20, 2020
Dhruv Khullar
Physician
"

Back to the Original Post questions:

Age limit for the presidency:

I agree with you (maryla) that it's hard to say, as it varies case by case. Also, the potential for a long, healthy, and productive life continues to increase -- though not evenly across the board for everybody -- the increase is mainly among the people with the resources and the habits to care for their own health.

Some 85-year-olds would be a lot better presidents than some of the prominent politicians who are much younger. If there is an age limit for the presidency, it should be pretty high, like maybe 85 or 90. Some people get wiser as they get older. Some get more experienced and more connected to other people who can help form a good government.

(Interestingly, not everyone _wants_ good government, but prefers to destroy the government.)

Term limits for Congress:

I think there should be term limits, but I don't know how long they should be. Reforming campaign finance, or reforming how campaigns are run, or how the media covers them, would probably help make a better Congress, more than changing term limits.

This is hard to say as its on a case by case basis.
Example 1: Biden He has had numerous conditions that have affected his mental capability to do the job. It is embarrassing when he attempts. I think it must be a Dem characteristic to go the costlier, less efficient way of getting things done. He is the oldest president I think and does little or no strenuous physical activity. on the other hand
2. Trump is also 80 and plays golf and is much more in shape, especially since his covid scare.

The thing here is that to be truly healthy, a time must be spent regularly to maintain one's fitness

...

- - - - - - - - - - - - - - -

"... Trump's Corruption" ??? Accusations from anti-Trump sources. Let's see some proof???

"On corruption claims, Biden cites facts while Trump tosses ..."

"'Complete incompetence': Biden officials fume after Trump ... Noooo, Biden (a known liar who claimed a stellar law school rating but was actually at the bottom of his class)( a known plagiarizer) accusing Trump of corruption and incompetence... ohhh, say it isn't so.

"CNN reports that Biden officials were shocked to learn that former President Donald Trump and his team never bothered to develop a plan for distributing the vaccine for the novel coronavirus..."Part of your problem is not checking on your sources. Try this one https://medicalxpress.com/news/2021-01-covid-vaccine-rollout-nears-million.html this was written Jan. 14. How, exactly, was it possible to distribute vaccines at the rate of a million a day without a plan?

- - - - - - - - - - - - - - -

Those results suggest that the more corrupt and incompetent president might be Mr. Trump rather than Mr. Biden. Tens of millions of Americans think so.

That's why they voted for Mr. Biden rather than for Mr. Trump.

Or, to put it another way, the results from the votes, the audits of the votes, and recounts of the votes, and the courts and the election officials, all indicate that more people voted for Mr. Biden than voted for Mr. Trump, and that fits with the very plausible idea that most Americans think Mr. Trump is more corrupt and incompetent than is Mr. Biden. Search results? Really? Do a search on 'grey aliens'. What do those results tell you?

President Trump has been the target of unrelenting attacks, smears and libel since before his nomination. He is the most investigated person in human history and they found NOTHING.

There is public video of Biden bragging about strong arming/extorting the Ukraine; 'you want the billion dollars, fire the Prosecutor; you have 6 hours or no money".

A personal question from me to you; How can you be so ignorant of the facts and so superficial in perspective and still get your fork to your mouth to feed yourself.

This is hard to say as its on a case by case basis.
Example 1: Biden He has had numerous conditions that have affected his mental capability to do the job. It is embarrassing when he attempts. I think it must be a Dem characteristic to go the costlier, less efficient way of getting things done. He is the oldest president I think and does little or no strenuous physical activity. on the other hand
2. Trump is also 80 and plays golf and is much more in shape, especially since his covid scare.

The thing here is that to be truly healthy, a time must be spent regularly to maintain one's fitness