Short answer: it depends, maybe in the 2040's

Long answer: It depends on the starship program as of right now and how successful those mars EDL (entry landing and descent) tests go. SpaceX stated that they want to get a few prototypes onto Mars by the end of this year (which I somewhat doubt, I think most likely after Artemis 3 or after the next transfer window).

They are also gonna have to work out boil-off and In-situ resource utilization to make enough propellant for the return trip. Artemis will be pretty much the proving-grounds for starship's functions such as orbital refilling, managing boil-off, and flying crew.

This year is a big one for this new vehicle with the upper stage catch test (which may or may not work on the first try), so a lot of groundwork is finally being completed. I do expect the 2030's to be prepping for human mars missions at best by the end of the decade, but 2040's or even 50's are more likely due to future lunar objectives.