Young gentlemen is an archaic term that was used in the Royal Navy to refer to boys aspiring to become commissioned officers, but who had not necessarily reached the rank of midshipmen.
[1] Boys aspiring to a commission were often called 'young gentlemen' instead of their substantive rating to distinguish their higher social standing from the ordinary sailors.
[2][3] Boys would join the navy around the age of 12 and they would serve as a servant for one of the officers, as a volunteer, or as a seaman.
[4] Occasionally, a midshipman would be posted aboard a ship in a lower rating such as able seaman but would eat and sleep with his social equals in the cockpit.
[5] HMS Bounty was limited to two midshipman posts, but it carried several boys who would have been rated as midshipmen aboard other ships, including Peter Heywood, and George Stewart, who was mustered as an able seaman but served as acting master's mate after Fletcher Christian was promoted to acting lieutenant.