There are various aptitude testing scheme available to aspiring aviators. Guild of Air Pilots to name but one. A good golf handicap is an excellent guide to ability.
I would suggest that your local club is perfectly capable of knowing if someone going through PPL training has what it takes to progress. That would be the best place to ask.
An obvious indicator would be completing successfully within minimum syllabus hours.
Taking 1.5 times as long might indicate a poor learning curve.
Any modular courses do require full time attendance unless you are particularly gifted.