Herman-Giddens and colleagues looked for two signs that boys had begun puberty: sparse pubic hair growth and an increase in the size of the testicles to 4 millimeters (at full sexual maturity, the testicles measure 25 millimeters).
Not buying it based on one study that looked for sparse hair growth. Puberty on average is 12-16. Unless my town is some outlier not many 12 year olds have gone through puberty. not that I'm a PSU fan checking
See my edit above...you glossed over "beginning". His link did not say 12 yr olds have gone through puberty.