Production for the Super Heavy booster won't start until Mk4 is complete, Musk added.

Despite that, crewed flight might come sooner than you think. SpaceX wants to pursue heavy reusability, to the extent that one Starship could fly "three or four times a day" while the booster could fly "20 times." That could help it prove the feasibility of the technology quickly and put people on rockets as soon as 2020. SpaceX had previously aimed for commercial service by 2021 and its lunar tourist trip by 2023, and those goals would be more realistic with humans flying a year earlier.

Of course, there's a lot that needs to go smoothly for this to happen, including an "exponentially" improved manufacturing process that, among other things, will use near-seamless rings of steel for the chassis instead of numerous welded plates. Musk is well-known for optimistic predictions, including his original hope that Falcon Heavy would fly in 2013. Don't be surprised if there are delays. SpaceX has advanced considerably since its early days, though, and it's evident that Musk doesn't want Starship to spend years in testing limbo.