Armin's answer is plausible, but I suspect not the obvious answer. Does it mean that nobody else wants to be a captain that he has to be the captain at a very old age? No. . More likely, it suggests that the lack of ambition is his. That is, he didn't want to rise, to become higher than a captain. So, he never became whatever comes after captain. So, he remained a captian.

Captains are usually younger so it was odd or unusual that he had no desire to progress higher than captain. This makes one to wonder why he was like that.

Yes and the curious means you wonder why such a strange happening could occur. The strange happening being no one wanting to be a leader since mankind typically wants to lead. Thanks and Jesus bless you.