OK Gaile, how about this. We can express either a birth date or a death date in four possible ways: exact [date], before [date], after [date], or about [date], so there are 16 possible combinations for which you're looking for wording. (This looks fairly straightforward if you show it in a 4 x 4 table, but as a by-product of this exercise, we have determined that I'm incompetent at producing a table for G2G.)
For the case of exact birth and death dates, we can state "Died at age [exact]." For the cases of 'exact' birth date and 'before' death date, or 'after' birth date and 'exact' death date, we can state "Died at age [#] or less". For the cases of 'before' birth date and 'exact' death date, or 'exact' birth date and 'after' death date, we can state "Died at age [#] or greater". And for the cases of 'exact' birth date and 'about' death date, or 'about' birth date and 'exact' death date, or 'about' birth date and 'about' death date, we can state "Died at about age [#]". For the other eight possible combinations, we adopt your suggestion of not attempting to report age at death in prose.