If someone is untutored, they have not been formally trained to do something, although they may be quite skilled at it.
例句
This untutored mathematician had an obsession with numbers...這位非科班出身的數學家對數字特別癡迷。They had left school at fifteen and were quite untutored in writing.他們15歲就輟學了，幾乎未接受過正式的寫作訓練。
英英詞典釋義
Adjective
1. lacking in schooling;
"untaught people whose verbal skills are grossly deficient""an untutored genius""uneducated children"