I think it's feasible to send a human to Mars by 2025, but that person wouldn't be coming back any time soon. Sending a person to Mars and back is only marginally simpler than the reverse task - sending a person from Mars to Earth and then back to Mars - would be. We know how difficult it is to send *anything* to Mars. Imagine how much more difficult it would be if, instead of having a huge infrastructure in place with launch pads and control rooms filled with technicians, and fire crews on standby, and the biggest boosters we can fabricate, all that we had available on Earth was what we could successfully land on Earth from orbit.
It isn't quite that bad, because Mars gravity is lower than Earth's, so we don't quite have to land a fully-fueled Saturn 5 there, but it's still a task that's at least an order of magnitude harder than going to the Moon and back, even before the longer travel time and longer signal transmission time is taken into account.
Nevertheless, I believe it's going to happen. People will go to Mars without any realistic chance or expectation that they will be coming back, and with no plan to bring them back. The pioneers of previous ages would set forth often without any reasonable expectation of return, and the same spirit will infuse some members of a future generation. I think the first person on Mars might be one with a terminal but non-disabling illness; there won't be such an outcry against an astronaut being sent on a one-way trip if that person's life expectation is severely limited anyway. Later astronauts will go as settlers, hoping to carve out a niche for themselves with prefabricated greenhouses.
It may seem inhumane, but, given that it's going to happen anyway, we should be planning for the first one-way human trip now, so it can coincide with the first sample retrieval mission. That way, the first human on Mars can collect lots of different samples from a variety of different locations, and pack them all carefully into the small return capsule, instead of all the samples coming from the same small area and being collected more-or-less haphazardly like they are with Phoenix.