Paragraph 6: At what age can a poor child become a semi-decent thief?

From the text:

They can very seldom pick up a livelihood by stealing till they arrive at six years old, except where they are of towardly parts; although I confess they learn the rudiments much earlier, during which time they can however be looked upon only as probationers, as I have been informed by a principal gentleman in the county of Cavan, who protested to me that he never knew in Ireland above one or two instances under the age of six, even in a part of the kingdom so renowned for the quickest proficiency in that art.