The date that a health condition affected your ability to work

Hi
My daughter is transferring from ESA to UC.
The application form requests a list of health conditions and the date that they affected her ability to work.
Since some of the conditions have existed from birth, others were diagnosed before her 18th birthday and others since then, what date should I enter?
There is a date, about 10 years ago, when she last worked.
Should I use:
Her birth date?
Her 18th birthday?
The date of diagnosis?
The date she last worked?
Other?
Many thanks for any input.
arb