Remember that if someone truly died at the age of 30 in 1900, they could have been born in 1869 or 1870 depending upon when their date of birth was in relationship to the date they died. If they were born on 4 March 1869, they would be 30 on any document in 1900 dated before 4 March and 31 on any document in 1900 dated on 4 March or after.
So if a tombstone says the person died in 1900 at the age of 30, they could have been born in 1869 or 1870, if only the years are given on the stone.
Whether or not the age is correct in the first place is another matter.
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