By my count Riker was offered his own ship four times that we know of: He was offered the Drake at the age of 29, but turned it down in favour of the first officer position on the Enterprise. He was offered the Aries a year later and turned down that ship too. Next was the Melbourne just before the Borg attack of 2366. Then the offer of the Titan rolled round fourteen years later in 2379. Starfleet may well have offered him his own ship between 2366 and 2379 - maybe they were offering him ships regularly from the age of 29 with the Drake to 44 when he finally accepted the Titan. Or Starfleet may have taken the view 'we''ve offered him three ships and had three refusals, he can stay on the Enterprise for all we care...' He was clearly a rising star within Starfleet, Picard described him as 'quite simply the finest officer he'd ever served with'. But his career stalled after a year or two on the Enterprise, he and everyone else around him knew that. To my mind he was essentially a captain serving as a first officer from about 2366 onwards after the Borg attack, after which his stock was probably as high as it had ever been after his field promotion and the part he played in stopping the Borg. Was he right to stay as long as he did? Curious to know what others think?