So, I've been playing for about a year now, and I still have not figured out what Twist means. Could someone explain?

Also, I don't understand the progressive Theme leagues that seem to only include past winners.

Twist is when you take a roster, and twist the players on that roster to any season you want.

Up until the salary explosion, the 08 Dodgers were a very popular choice among twist leagues as it had a rookie Kershaw to go with vets like Greg Maddux, Derek Lowe, Takashi Saito, Nomar Garciaparra, Manny Ramirez, Jeff Kent, among others

To expand on that example, you could start with a real-life roster like the '08 Dodgers and use any player that was part of that roster, but twisting allows you to use any season in that player's career, not just the '08 Dodger season.

Progressive leagues are leagues that play usually in a historical sequence - say, starting in 1950 and then drafting new players that appeared in 1951 while retiring those that retired after 1950. The owners usually are around for a long time because the whole point is to follow history, though there are sometimes variations. Regressive leagues start at a historical year, say 1950 and play backwards in time, so players "retire" after their real life rookie year. I think that is what your question referred to.

There are some theme leagues that are only for owners that have reached a certain level in terms of winning championships in other leagues, though I have never played in one and don't know.

As to twisting:
https://www.youtube.com/watch?v=im9XuJJXylw

Oh, just kidding, it's what those guys said above.

Progressive leagues will often have "past winners" in their official league description, because progressive leagues cannot be explained sufficiently in just that description, and anyone going into the league knows the description is not actually the description...

Thanks everyone for the info!