many factors
1) better competition, more grapplers
2) PED testing
3) cage & elbows
I believe he was only like 31 or so at the time. The age/injury/longevity in kickboxing/mma excuse is bullshit. guys like semmy schilt & peter aerts, mark hunt have been through much worse and won titles at 37+ in kickboxing (except hunt). HWs usually last the longest out of all classes because the only real detrimental factor is speed and durability, which until 35 would not be noticeably different
Even right now at LHW/HW, belfort, rashad, rampage, teixera, machida, frank mir, bigfoot, DC, gonzaga there all pushing 34-36 and there prime was when they were around the same age cro-cop entered the UFC (30-33) just a few yrs later. liddell & silva were both champs at 36 & 37, hughes at 34
guys like tex, shad, machida, DC, belfort .etc, there all still revalent in the top 5 despite being about 35 or 36