Does aeronautical experience ever expire? Do the hours of flying with instructor or solo ever expire? I have my 50 (yes, 50) year old pilot's Flight Log with CFI entries for 20 hours dual and 1 solo. Do I have to start over, or would some of them count for PPL license?
As far as the FAA is concerned, they do not expire.

As far as any (reputable) flight school goes, they will probably require a full, recent minimum 40 hours of training before they sign you off for the practical exam.

The good news is that your old training, no matter how rusty, probably means you'll pick up the basics quite quickly, and probably solo (again) faster than the average, and may very well be ready for your checkride close to 40 hours.  (The national average is a checkride around 50 to 60 hours.)