There's a good answer to this already that the OP is quite happy with. However, I strongly feel that the framing is vague and misleading. So I'd like to see us have an answer that's a bit more explicit.
Oldest Major Party Nominees:
Below are the oldest people to have recieved a nomination from what was at the time one of the 2 major parties.
Name |
Age at Nomination |
Election Year |
Donald Trump |
78 |
2024 |
Joe Biden |
78 |
2020 |
Donald Trump |
74 |
2020 |
Bob Dole |
73 |
1996 |
Ronald Reagan |
73 |
1984 |
John McCain |
72 |
2008 |
Donald Trump |
70 |
2016 |
Oldest Serious Nominees
Where a "serious nominee" is someone who was nominated by a party, actually mounted a campaign, and either received Electoral College votes or was on the ballot in all states that had ballots at the time.
Name |
Age at Nomination |
Election Year |
Donald Trump |
78 |
2024 |
Joe Biden |
78 |
2020 |
Donald Trump |
74 |
2020 |
Bob Dole |
73 |
1996 |
Ronald Reagan |
73 |
1984 |
John McCain |
72 |
2008 |
Donald Trump |
70 |
2016 |
Note that this is the same list
There are a couple of people who nearly made this list. Samuel Adams did receive electoral votes. However, US political parties did not give out "nominations" at that time, and he was a member of the same party as multiple other people who received Electoral College votes. Likewise, Harry Byrd in 1960 also received electoral votes without the benefit of any party's nomination.
Oldest Party Nominees to get 1%
This is the same list as the above 2, with the addition of 73 year old John Bidwell, who got a whopping 2.24% in the election of 1892 as the nominee of the Prohibition Party. That slots him in the table right under Ronald Reagan. He received no Electoral College votes, and was not on the ballot in all states.
Oldest Party Nominee
I don't think we know this one, and I don't know that we can know it. Every cycle hundreds of people "announce" they are running for President, and make themselves "parties" to make it look like a real campaign. For instance, comedian Pat Paulsen started a "campaign" as part of a comedy bit on the Smothers Brothers show, and kept doing it for multiple cycles thereafter. It was a good bit, allowing him to lampoon politicians during election seasons (a much-needed service).
Another such perennial candidate is Vermin Supreme, who has run as the nominee of the "Good Humor Party" and the "Free Pony Party". He's 64 now, and will presumably keep running in the future, health allowing.
Other people often mount symbolic campaigns to get media awareness for favorite causes. This was certainly the case for Willilam Hope Harvey, mentioned in the question. His "Liberty Party" was created to promote his own economic theories. (Note that his party merged with another during the election, so he ran as an independent, not a party nominee)
Then some people (actually, a whole lot of people) are just downright mentally unwell. I'm not adding examples here so as not to signal boost them.