don't push too much...
The question is: I understand that a domain, say registered 1 day ago, costs nothing.
But if we assume that I registered the SЕX.COM domain yesterday, it costs much.
What is the meaning of the domain "age"?
I think the age of the domain is important in cases where you need to show solidity and add a level of reputation.
For example, you create a company this year, and write on the website that you have been working since 2008. In this case, take the domain registered in 2007-2008.
Then the one who enters the site does not have any dissonance. Everything seems to be correct, they have been working since 2008 and the domain was taken at the same time, everything is ok.
Personally, I so often check where they write that they say they have been working for many years.
But, I think there are still few such knowledgeable people, and this is not a 100% guarantee, because the domain could be changed in the process of activity.
I don't see any other advantages for old domains.
Many people think that unique and close to the topic domain names are worth a lot, but with the advent of 202x this rule does not work, of course there are points in this, but not at all like it was in 2014.
About age. Everything is complicated here. Of course, mothballed domains, for example from 2017, will cost significantly more than those created at the beginning of the year, but you should also take into account the traffic of the project and its "topic". On some interesting services, such as "chronicles" and "backup records of the Internet", you can find all this information.
If you want to know which domain and domain name is considered old enough, then I would say 6 years. 6 years is the age to trust.
Even if several web sites of the same topic have the same relevance, the search engine still gives preference to one relative to the others, placing them in higher positions in the output list. That happens, among other things, because the ranking algorithm takes into account the age of the domain name, i.e. "old" web sites that have existed for more than 1-3 years are more likely to be in the top than newly created young sites.
The age of the domain name is not an unimportant indicator of the domain that search engines take into account when ranking.
The older the domain, the more trust it has, the more likely it is to get into the top search engine results.