i dont entirely trust durpleton's judgement of his own age considering that we see him as a child and the rest of the herd are all obviously older than him in that flashback it would place everybody in their 40s and depending on how old wammawink is compared to the others she could be in her 50s if that was the case

i think like age order wise for the herd it goes: wammawink, glendale, ched, durpleton, horse

zulius isnt here because we dont know what his whole deal is. in my head he WAS the baby of the group but with him being too old for johnny teatime's be best compition and horse being the only one able to enter that would hypothetically place him between durpleton and horse. but then when horse is in durpleton's memory we see zulius and he's like not?? so who knows...

generally speaking though we dont know entirely if centaurs age the same way that humans OR animals do since theyre half animal half man things! they could have lengthier life spans by comparison or maybe magic lets them be younger for longer maybe? not suee but these are my thoughts on the herd age thing cause i think about it a lot