It's just a number I chose. It seems that every really good snooker player (the top pros at least) start playing around the age of 8 or 10 and then turn pro around 18 or so and then keep improving to their mid-20's or so and then after that the long potting starts to go a little bit and I figure this is the hand-eye coordination going.
The real reason I picked 25yrs is in the table tennis world they say you are past it at 25yrs because of the loss of coordination. I watched a world-class table tennis match with a couple of Chinese players and I can understand why seeing them smashing that little ball from 20ft away from the table.
I think in snooker it really starts to show around 35yrs or so. The other thing is kids learn so fast (maybe because their brains are relatively empty compared to an adult or something) but young kids learn everything fast, especially languages and sports skills. Didn't Tiger Woods start when he was 3yrs or something?