I think disese resistance can play role in this, too. they are known for being very disease resistant, so in turn their immune systems do not break down or decrease in effectiveness as much as other breeds might over the lifetime of the cow.
I think there are many factors to their longevity.... also coming to mind is that they were open range cattle where it was survival of the fittest and the stronger ones lived longer.
Good topic here. I find it amazing how the best judge of efficient grazing animals, no matter how many trials we do or how much research we document, is still good old Mother Nature. There's no denying she has the best eye for stock.
We seldom ever join our females before they are two. They grow much better when they are allowed to get over the adolescent stage. With breeds like ours there is plenty of time to have a long breeding life. So whats missed out presumably at the beginning you gain at the end.
Environmental factors are a big consideration,availabilty of feed etc.
Ours are all british and mature at 1300-1500 lbs, carry good flesh, wean good calves, and they all calve at 23-24 months. I sure don;t think I'ld want thme to "grow better".
Genetics and selection! Frnstance, weaned at 560 (drought year) bred @ 1036 (still a drought year) calved @ 1204 23 months of age.
With the average type of native grazing here I wouldn't expect to have to cull for teeth wear before 15 years with Tuli, and an appreciable number should go to 20 years, I had really hard grazing in Africa,but my in-laws on similar grass to what I have here in N.C. have cows well over 20 years in their stud.