Oy! I read the help too quickly and didn't test the age calculation. I apologize for the oversight.
"Yellow" dates do show up in reports. If I were faced with 29 February 1900 I think I'd enter it as "29 February 1900 Julian" & put the sort date to 28 February 1900. If I felt that reports needed an age calculation I'd edit the sentence templates appropriately. As to the on-screen display, age calculation is pretty easy if one starts with 1900 .