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 [1]
Deceased persons, corporations, or groups of persons
Recently 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 [2]
FabC