We started ours this past January, about 6 months out from the wedding. You can always start earlier, but you'll need to go through and readjust your registry as things get discontinued/get sold out/etc. Even in starting in January, I've already had to go and find a couple of replacements for things that are no longer available.
We didn't create a registry. We don't like the idea of burdening people into buying items from a list. Instead we created a SoKind registry where people can donate money to a local charity that helps rescue and take care of domentic animals.
We started ours about 10 months out because a lot of people were asking for our registries. But I wouldn’t recommend that far in advance because a ton of things were discontinued so we had to constantly update it!
Our wedding is this weekend, and I think we had ours done in June. I did end up adding another registry in December, though. One of my shower invitations said I was registered at Target, and I wasn't so I made one so people wouldn't keep asking where that registry was lol. It was used a ton so I'm glad I added that one!
We created our registries right away and kept adding to them until we made them public. This way we had a lot of time to think about what we wanted. You don't need to go into the stores to start them these days! We started almost all of ours online. But, we started our Crate & Barrel one in the store because my fiancé is old-fashioned like that, haha.