Fourteen years, Tim, not forty! The lines are:

For fourteen years and over I've ploughed the ocean wide

and

If I was but ten years younger and she as old as me

...which is ambiguous, but can perfectly well be taken as indicating that he is only ten years older than she is; which, assuming he started at sea at the age of (say) 13 or 14, would put him in his late 20s and her, arguably, in her late teens: and, from his point of view, still a child. In the other two known versions, David Marlow sang 'fifteen years and over', while William Garratt sang 'fifty years and over', but that was probably just a mistake for 'fifteen'. I don't yet know of a broadside version of this song, but I'd expect it to have appeared in cheap print during the 19th century. If something comes up it may clarify the original intent.

On another point, I hadn't realised that Carl Watanabe wrote traditional songs. He must be a lot older than Tim thought that sailor was, if his lyric is in any way relevant to the question 'Saro' asked. There is no shortage of modern songs on 'taboo' subjects.

There is a recording made by John and Ruby Lomax of 'There Was a Lady Loved a Swine', sung by Kate W Jones, Houston, Harris County, Texas, 10 April 1939, at The John and Ruby Lomax 1939 Southern States Recording Trip. The words are in the DT as: The Lady that Loved a Swine. As it survives, it is a harmless nursery rhyme (and published as such in children's books), though it seems to have been just a little raunchier back in the 17th century. Did Charley's uncle have a pornographic version, by any chance?