There are still many medical issues that need to be resolved, and unlike the technological ones, these issues may make prolonged exposure to weightless conditions a lethal hazard. Astronauts in orbit for more than 100 days return to Earth in terrible physical condition. A 1-way trip to Mars takes over 250 days. The following is my table for putting a person on Mars in terns of the probability of this event up to the indicated year. It is a gut reaction based on where I gather the medical and engineering technology is. I give a probability for the actual landing, and for when we have ironed out the medical and engineering problems, and assumes the Space Station accelerates the solution of medical problems:
Landing Technology
Year Probability Problems solved
1999 0.0 10.0
2005 1.0 20.0
2010 10.0 40.0
2015 25.0 100.0
2020 40.0
2025 60.0
2030 80.0
2035 90.0
2040 100.0