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.