Some years ago while looking at statistics for world class weightlifters from the 1980s, I thought I saw an almost direct relationship between age and weight class, with the top lifters in the lightest classes being around 20 years old, and those in the superheavies being around 30.
It surprised me a bit at first, but seemed to make sense: a 52-56 kg lifter would have finished growing and filling out before a superheavy. And those in the upper weight classes also have more room to play with in terms of adding muscle mass etc.
However, I just took a look at the rankings for 2006, 2007, 2008 at www.iwf.net, and it turns out that the superheavies generally don’t peak at 30-32. Most are younger than that.
There does, however, seem to be a correlation between age and peaking or longevity. In 2007, four of the world’s top ten spots among the superheavies were taken by guys 30 years or older (Scerbathis, Jaber, Najdek, and Kleszcs) (there was a tie for third place, so you could say four of the top eleven were 30 or older.
A quick look at the lightest weight classes suggests that it is very rare to see anyone of that age among the top ten.
So it might be more accurate to say that super heavies have more longevity and/or peak in the mid to late 1980s. Someone could crunch the numbers and figure it out without too much work.
Good catch by the OP, though.