Flying on average about one hour per week I completed my PPL in almost exactly a year. The weather was a problem during the winter, I sometimes went for three weeks without flying, although in the run up to going solo I managed to get flying on a more regular basis.
By the way I'm not sure I'd recommend doing a JAA PPL in the US, the flying is great out there but personally I think if you're doing a licence that's to be used in the UK then it should be done in the UK.