I think it is reasonable to believe that - if there are no blockers uncovered, just steady development and testing - they could be testing it in space by mid-year and have it working by year-end.

Then - as long as fuel storage in space works - I do not know of any other major impediments to launching an unmanned Starship mission to Mars.

Sticking the reentry and landing will be hard, but Starships seem to handle tough reentries well, and Starships have already landed on legs on Earth.

I am a pessimist on a manned Starship landing on the Moon within three years, let alone on Mars.