when was patient 20693's first operation since 3 years ago?
select procedures_icd.charttime from procedures_icd where procedures_icd.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 20693 ) and datetime(procedures_icd.charttime) >= datetime(current_time,'-3 year') order by procedures_icd.charttime asc limit 1