We don’t have much information about Daeron’s youth, so it’s hard to say. But the Oakenfist seems to have best fit the bill as a mentor figure – he was a good thirty years older than Daeron, already a storied (and daring) naval commander, and was heavily involved in Daeron’s planning for his Conquest of Dorne. 

But given his extreme youth at the time of his great victories, I think we have to assume that he was a prodigy, because an average student even of a great teacher wouldn’t have been able to do what he did in the time he had.