I doubt a timeskip will come. All timeskip speculation comes from Oda saying this (War and movie) is the last adventure of Luffy as a 17-year old. Then a lot of rumor about a timeskip, including an April Fools joke by Greg, who claimed Oda confirmed the timeskip in an interview, began to circulate.
If there's a timeskip, it will probably not happen in the middle of an arc. So I don't see it happening after the flashback. This is not DB, in which the characters would train for one year for the next tournament or because some big enemy was coming. The characters in OP have no reason to sit on their asses for one year or more; instead their priorities should be finding each other. That's why I don't think there will be a timeskip any time soon.
IMO, Luffy will turn 18 in-story, and the next comemoration of the crew together will be their first year as pirates.
–-------------------------------
About the "poop age".
To me, One Piece never had a poop stage. I liked it since the beginning. The first chapter I read as #1 and never stopped since then. Things were calmer and simpler back then, but it was still awesome. Oda used those adventures as a warm-up, with the series hitting full throttle by the Arlong Arc.
And to stay on-topic, Hancock will join, you can bet your asses on that.