In this context, Robert is clearly a suffer of Polio and he has a disability. But for the first time he is now able to move around the house. He is also now able to go somewhere - i.e. actually leave his house and visit a town, or another place for example. He has clearly regained some mobility. So as an example, we can move around a house... i.e. we walk in the rooms of the house and from one room to another. And we go from one place to another.. i.e. We go from one town to another town. We travel from one town to another town. WHEN AND ANYTIME In this context "anytime he wanted" is just as valid as "when he wanted" However "anytime" is a stronger word in this context and emphasises that Robert now has true control of his mobility and has a new freedom.