Questions about Nicholas Biddle's early naval career

A comment questions a simple account of Nicholas Biddle entering the Royal Navy at twenty after seven years at sea. If he was an American seaman, the earlier experience may have been in Caribbean merchant service, and a rapid rise to master's mate would still need explaining. One possibility raised is that Biddle earned money teaching navigation, which could account for contact with Nelson, but this remains speculation. His almost immediate promotion to command a fourteen-gun brig in the Continental Navy further suggests that the compressed biography leaves out important experience. The exchange tests the received story against rank, training, and career timing.