My advice (sorry it's different) would be to start now, if your instructor is willing. You'll have the benefit of greater instructor and airplane availability. Also, flying isn't going to be any cheaper in the spring.

Finally, there will be plateaus in your training and learning. When I'd have people start in the spring, oftentimes a plateau at the beginning of summer would mean I wouldn't see them again until fall (when someone gets frustrated or bored, it's easy in summertime to concentrate on other things). At least in the wintertime it'll be something for you to do.