There have been a number of studies in recent years about girls reaching puberty at a younger age but now this study is saying the same about boys. There needs to be a lot more research into the cause(s) of this change but weight may be part of the issue. The Guardian:
Now the AAP study, officially unveiled at a national conference in the US, is showing the same trends in boys. It primarily identified the signs of puberty as the growth in size of testicles and largely shied away from speculating on what may be causing the shift, though it did refer to changes in diet, the fact that modern children are becoming less physically active and other environmental shifts.All that has led to speculation that weight gain might be a possible factor. It certainly might explain the earlier development among girls, as body fat is linked to production of the female hormone oestrogen. But the link might be less clear with boys. Also, it is not certain if weight gain is a trigger for puberty or simply a consequence of it.
The investigation also showed that American boys are divided by race when it comes to puberty. It found that, on average, black American boys started showing signs of puberty at a little older than the age of nine, while their white and Hispanic counterparts did likewise just after turning 10.