Date: Monday, August 4, 1788
Paper: Litchfield Monitor (Litchfield, CT) --obtained on Genealogybank.com
Angus Nickelson wanted an apprentice in 1788 to learn the art of bookkeeping.
Angus wanted the boy to be able to write and understand the rule of three (meaning he could solve basic proportions). This would help him in determining various amounts to charge for items based on a specific price and obviously a bookkeeper in the 1780s would need to know how to write.
What I found interesting was "None need apply from less than 20 miles distance from this place." I'm not certain why this phrase was included in the ad.
Is it possible your ancestor traveled a distance to become an apprentice? Are you ignoring a connection because the distance was too far? This ad indicates that may not have been the case.