It's probably a combination of age and frequency of flying. I've been studying for PPL for over 2 years now! Currently at 37 hours, estimating PPL at around 50 hrs.
Anyway, went solo last July at 14hr 45mins (my club average is about 17 hrs), aged 24, having averaged about 1 hour per month up 'til then.
If I'd done it in a more intensive time-scale, without all the relearning each time I'm sure I could've done it quicker.