Try this!
concat(ifelse(floor(dateDiff({employee_start_date},now(),“DD”)dateDiff({employee_start_date},now(),“DD”)/365)>1,concat(toString(floor(dateDiff({employee_start_date},now(),“DD”)dateDiff({employee_start_date},now(),“DD”)/365)), ’ years, ‘),floor(dateDiff({employee_start_date},now(),“DD”)dateDiff({employee_start_date},now(),“DD”)/365)>0,concat(toString(floor(dateDiff({employee_start_date},now(),“DD”)dateDiff({employee_start_date},now(),“DD”)/365)), ’ year, ‘),’’),
ifelse(floor((dateDiff({employee_start_date},now(),“DD”)dateDiff({employee_start_date},now(),“DD”)%365)/30)>1,concat(toString(floor((dateDiff({employee_start_date},now(),“DD”)dateDiff({employee_start_date},now(),“DD”)%365)/30)), ’ months, ‘),floor((dateDiff({employee_start_date},now(),“DD”)dateDiff({employee_start_date},now(),“DD”)%365)/30)>0,concat(toString(floor((dateDiff({employee_start_date},now(),“DD”)dateDiff({employee_start_date},now(),“DD”)%365)/30)), ’ month, ‘),’’),’ and ',
ifelse(floor((dateDiff({employee_start_date},now(),“DD”)dateDiff({employee_start_date},now(),“DD”)%365)%30)>1,concat(toString(floor((dateDiff({employee_start_date},now(),“DD”)dateDiff({employee_start_date},now(),“DD”)%365)%30)), ’ days ‘),floor((dateDiff({employee_start_date},now(),“DD”)dateDiff({employee_start_date},now(),“DD”)%365)%30)>0,concat(toString(floor((dateDiff({employee_start_date},now(),“DD”)dateDiff({employee_start_date},now(),“DD”)%365)%30)), ’ day ‘),’’))
This might not be exactly right because some months are 31 days instead of 30. But let me know if that helps.