It's certainly possible that we might visit Mars, but colonizing it just isn't possible within the foreseeable future, certainly not within Musk's lifetime. We're not even close to having the technology necessary to survive that kind of journey and the engineering, logistics and medical science required to actually start a colony is far beyond anything we are currently capable of.
Colonisation of Mars is going to be a long process. There is going to be a gap of decades (maybe even more than a century) between the arrival of the first settlers and the attainment of self-sufficiency (autarky, the ability to survive without continual resupply ships from earth). From my reading of Musk's various comments, he doesn't think it is likely he'll live to see self-sufficiency (autarky), but he certainly hopes that the arrival of the first settlers can happen in his lifetime.
