It doesn't, obviously. Potentially there's still another year to wait. But it never hurts to be reminded of what a massive project scheduling cock-up this has been.
But even if you can't yet ride Crossrail, you can already buy a ticket.
Pop down to your nearest TfL station, find a TfL ticket machine and request a ticket to Woolwich. This shouldn't be possible, because the station doesn't yet exist. But the machine will happily sell you a ticket anyway.
Don't rush out and try to bag yourself a souvenir. Tickets from TfL ticket machines don't include a destination, only the station you bought it from, a fare and a date. Your ticket will be perfectly valid to wherever, but it won't mention Woolwich.
I checked at several different stations, and all the machines were willing to take my money. The price is £4.90 for a single ticket from Stratford, Whitechapel or North Greenwich, for example, rising to £5.90 from stations in Zone 1. Return tickets cost twice as much.
Don't worry about how expensive this is. The price of cash tickets is artificially inflated to encourage people to Pay As You Go instead. This isn't a Crossrail-specific issue.
Although selling premature tickets sounds insane, there is a good reason. The software which runs TfL ticket machines is very complex, so is only updated a handful of times each year. The next update is in January, when fares rise, but this would have been too late for Crossrail's December launch, so the change had to be implemented as part of the previous update in September. The precise date was September 2nd, just two days after TfL announced Crossrail's launch was being delayed, by which time it was too late to stop the planned fares rollout going through.
Other Crossrail-specific tickets are available, for example to Abbey Wood, even though you can't yet follow the cheaper Crossrail routing.
In reality Woolwich station is nowhere near complete, just another unfitted box behind a hoarding. Indeed there was every chance its opening would have been delayed even if the rest of Crossrail had launched on time.
But you can already buy a Crossrail ticket to Woolwich, because life is strange.