HappyEndings: In biological terms, he was seven when he came through the tree. (It says so in the newspaper articles they show.) But who knows how long he was a wooden boy before then? And the original story does have him traveling to Pleasure Island; portals DO exist in the EF and some people use them regularly (like Rumple and Regina, who use Jefferson a lot). The problem is that such portals don’t go to places without magic. NL seems to have magic.
Jefferson knew a lot–partly because he spent time working for Rumple and Regina back in his portal jumping days. Although, yes, he had the whole curse to work out the Belle thing, I think he knew about Belle before the curse–and I daresay that she was Regina’s best-kept secret (she would have to be), and not exactly something that Rumple blabbed about a whole lot (though he did tell Regina about his promising maid and David that he’d been in love once and she was dead). It’s plausible that Hook found out about her through Jefferson, actually. With his travels, he could have learned quite a bit.
Though he didn’t know why Rumple wanted to go to a land without magic (why would anyone want that?), he did know that Rumple was seeking a path.
What isn’t yet clear, but what will surely be made clear next season, is why Rumple didn’t go to NL to get Bae if there is magic there. (Or why he didn’t succeed if he tried.)
Keeper of Belle's Gold magic, sand dollar, cloaks, purple FTL outfit, spell scroll, library key, copy of Romeo and Juliet, and cry-muffling pillow, Rumple's doll, overcoat, and strength, and The Timeline. My spreadsheet: https://drive.google.com/file/d/0B6r8CySCCWd9R0RUNm4xR3RhMEU/view?usp=sharing