On FactGrid we created two properties for this (maybe clever, maybe daft): P290 and P291 for estimates (or for knowledge) of an earliest and latest point in the life span. The necessity is here that we have loads of people with just a single data point like "studied in Jena in 1776" or "appeared on a list of voters in 1849". If that is all you know, you do actually know that the person is likely to have a birth date some 17 (or in the voters case at least 21) years before.
If a person is only once mentioned as retired that stretches the P290 date to some 60 years before and so on - you qualify the estimate accordingly.
I have no idea whether this is a good move on our site since we are not really that advanced in running the more intriguing SPARQL searches.
> Fabrizio Carrai <email@example.com> hat am 19. September 2019 um 22:13 geschrieben:
> So, the question is if it would be fine and ethic to set the "Date of
> death" to "unknown" on the base of an old date of birth.
> And about the biography of living persons, I found this 
> Deceased persons, corporations, or groups of personsRecently dead or
> probably dead
> Anyone born within the past 115 years (on or after 19 September 1904) is
> covered by this policy unless a reliable source has confirmed their death.
> Generally, this policy does not apply to material concerning people who are
> confirmed dead by reliable sources. The only exception would be for people
> who have recently died, in which case the policy can extend for an
> indeterminate period beyond the date of death—six months, one year, two
> years at the outside. Such extensions would apply particularly to
> contentious or questionable material about the dead that has implications
> for their living relatives and friends, such as in the case of a possible
> suicide or a particularly gruesome crime. *Even absent confirmation of
> death, for the purposes of this policy anyone born more than 115 years ago
> is presumed dead* *unless* reliable sources confirm the person to have been
> living within the past two years. If the date of birth is unknown, editors
> should use reasonable judgement to infer—from dates of events noted in the
> article—if it is plausible that the person was born within the last 115
> years and is therefore covered by this policy.
> This would support the set of "Date of death" to "unknown" on the base of
> the "Date of birth". It remains hard to verify typo errors, but we are
> doing our best to verify the data of the several wikiprojects.
> The property set would become effective if done in mass by a bot or similar.
> By the way, I would extend be period to 122 years 
>  https://en.wikipedia.org/wiki/Oldest_people
> Il giorno gio 19 set 2019 alle ore 21:29 Andy Mabbett <
> firstname.lastname@example.org> ha scritto:
> > On Sat, 7 Sep 2019 at 07:53, Fabrizio Carrai <email@example.com>
> > wrote:
> > > I found athletes with the "Date of born" but with NO "date of death".
> > > So a query on the age show me athletes up to 149 years old.
> > > Since the oldest know person was 122, what about to set "date of
> > > death = unknown value" for all the persons resulting older such age ?
> > Yes, but check that the date of birth isn't a typo (i.e. 1875 instead
> > of 1975; or 1894 instead of 1984).
> > Showing a living person as being dead would be a serious breach of the
> > BLP policy.
> > --
> > Andy Mabbett
> > @pigsonthewing
> > http://pigsonthewing.org.uk
> > _______________________________________________
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