My maternal grandmother, Ida Glouberman, was born on January 1, 1911, so she would be 100 years old today if she were alive.
Note, though, that I’m not sure how well this statement stands up in light of Russian calendar reform (see here for general interesting issues about the Soviet calendar). To bring the Russian calendar in line with the calendar in the West, January 31, 1918 was immediately followed by February 14, 1918, so 13 days were dropped.
We celebrated my maternal grandfather’s birthday on September 12 (he was born in 1898 in modern-day Belarus), but apparently this was New Style; that is, when he was born a calendar in the West would have read “September 12” but a calendar in Russia would have been something like August 31.
So if this is right — if contemporary Russians all “modernized” their birthdays — that means that when my grandmother was born, it would have been January 1, 1911 in the West, but December 19, 1910 on a Russian calendar, and she would have started calling her birthday January 1 after 1918. So we’d be correctly celebrating her 100th birthday today.
But would everyone have modernized their birthday in the same way? If your birthday was December 19 on a Russian calendar, you’d be happy to modernize it to get an awesome date like January 1. But if your birthday was already the awesome January 1 on a Russian calendar, mightn’t you be loath to change it to January 14? I don’t know how fluid birthday modernization customs were back then — maybe, with a Revolution and Civil War going on, they had more important things to do than police people’s self-reported birthdays? — and I don’t think we have any old documents to check.