One thing comes to my mind concerning a crewed Mars landing, the vast quantity of propellants required. Roughly 90% of the lift off mass is propellant and perhaps less than 5% is actual payload. And most of that "payload" is in fact more propellent for launching the ship from Low Earth Orbit to Mars. So in one way the atmosphere of Mars is actually quite handy in that you don't need to bring yet more propellant to land on Mars. Not to say it will be easy it won't, but it is just about manageable. On the Moon this is not possible so even more propellant has to be used to land.two things come to mind when considering a manned landing on Mars 1) the distance 2) the atmosphere. the distance part can probably be worked out since astronauts are now spending months on the ISS, still though if there were a problem they could return to Earth quickly since the ISS is in relatively low orbit- Mars on the other hand is 6-9 months away. Although physics is not one of my strong points , I would think having to go though Mar's atmosphere would be alot more difficult than landing on the Moon with no atmosphere to contend with.
Will humans be walking on Mars by 2024? IMO no its too soon and there's too much still to do. Perhaps only a very slim outside chance of a robotic Starship landing in 2024 followed by a crew in 2026. Much more likely would be a crew landing on Mars in the 2028 - 2033 time frame. I find people tend to overestimate what can be achieved in a year but under estimate what can be achieved in a decade.