Maximum Orcish biological lifespan in this setting?

Question

I'm working on a short story, and I plan to put some ancient Diremen in charge of the vast majority. (Please note that Orcs are called Diremen in this story) . Diremen have a variety of biological differences to humans, and I'm hoping to give them a realistic age for these elders.

Diremen can't die from old age. Instead, they continually grow until they simply can't get enough food and water or get crushed by their own weight. (Edit: They grow at 8 inches per year until 8, at which point they slow to 4 inches per year until death.) They reach adulthood at 8 years old. Diremen are also blessed with strong regeneration, fast enough that they can heal broken bones in only hours. Diremen also age very well, a non-direman usually can't tell much of a difference.

Diremen are mentally connected in a mental web they have no control over, which itself is connected to a hellish realm partially linked to the material one. This means that the Diremen can hear one another's thoughts and feelings, as well as a demonic realm. This drives many of them to be less stable, but a mentally powerful direman can use this to control other diremen with instincts.

While most diremen die at a younger age from conflict and accidents, these elders would be in a relatively safe place, so they'd only need to worry about biological death. While they could be backstabbed/challenged for the spot in the hierarchy, for the purposes of the question we don't need to worry about that.

Answer 1

Starvation dieting:

This is a bit of a frame challenge. While continuous growth is a problem, it seems likely there is some kind of special diet that would stunt Direman growth (and possibly seriously alter other parts of their metabolism) without actually killing them.

Perhaps they need a diet almost completely free of calcium, preventing bone growth. maybe they need an artificially-induced case or rickets. But come up with a sufficiently harsh diet, and growth will be halted.

Children who suffer nutritional deficiency are obviously seriously stunted in growth, but frequently survive such deprivation. Adult humans have stopped growing, and the growth-type deformities associated with nutritional deficiencies are not as significant. Caloric restriction is strongly associated with increased longevity.

Perhaps there is some terrible physical cost to such nutritional deficiencies that gradually deforms the Diremen who are sheltered and allowed to become elders. At the very least, they would likely suffer hunger and desperate cravings, so only the most disciplined individuals (who also, BTW would be the ones most resistant to the influence of demonic forces) would be chosen.

If you want to be gruesome, these individuals could gradually have arms, legs, and other tissues gradually cut away to prevent diet cheating and reduce the effects of the diet on the body. The diet would cripple regeneration. Eventually, they wouldn't be much more than heads with organs to support them.

Answer 2

Conservative Limit 30 years. Optimistic Limit 50 years

Figure A: Large Biped

A large tyrannosaurus could reach 6 metres tall and much longer from snout to tail. There are not many other bipeds that tall. So lets take 6m as a the maximum possible height. Then it takes an Orc 51 years the reach that size.

This is an optimistic upper limit, however, considering T-Rex lived at a time when there was more oxygen in the atmosphere. About 35% compared to 21% today. This means in today's world it would slowly die of brain damage.

Of course there are MANY differences between a human (orc?) and a T-Rex, and reasons you cannot simply scale up a human to be 6m tall and have them survive. For an overview see the top answer to this question and the links therein. Deciding orc biology to deal with these problems is left as an exercise to the reader.

Perhaps some of the reasons can be overcome using how an orc is smarter than a big smelly bird lizard. For example the issue of getting enough food. Orcs might farm to get enough food, be herbivorous, or simply have smaller orcs gather food for the big ones.

Figure B: Large Bipedal Mammal.

Megatherium could reach 6m long and 4m tall. Here is what it looks like once you eat all the meat.

These guys are warm blooded which makes them closer to humans than T-Rex. They still have differences, however, being herbivorous. This gives them a predicted temperament similar to modern tree-sloths. In any case your growth rates give an orc reaching 4m tall at 31 years.

Answer 3

Here is a link to images of elephants standing on their hind legs.

https://www.alamy.com/stock-photo/elephant-standing-hind-legs.html

Many are captive Asian elephants (Elephas maximus) trained to do so.

One large male Asian elephant in a circus was trained to walk for hundreds of feet on his hind legs, with a woman standing on his tusks.

Some of the images are of wild African Bush elephants (Loxodonta africana) standing on their hind legs to reach high branches with their trunks. This is done by big old males, the largest elephants. I expect that sometimes the tops of their heads reach about 20 feet (6.096 meters) above the ground.

Of course elephants don't and can't spend all of their waking hours standing on their hind legs.

The anatomy of elephannt like creatures would have to be rearranged for constantly standing and walking to be practical for them.

Giraffes sometimes get up to about 18 feet (5.486) tall, and their heads would be a little higher if they stood on their hind legs only.

So I can imagine a mammalian being that looks vaguely like a cross between a giraffe and an elephant standing on its hind legs reaching and exceeding 6 meters in height.

This site claims that some quadruped dinosaurs could raise their heads to great heights. In the extreme cases 70 feet (21.33 meters) and 84 feet (25.63 meters)

https://theverybesttop10.com/worlds-tallest-dinosaurs/

In some cases they might have confused the horizontal length and the maximum height.

But certainly some sauropod dinosaurs were orver 20 feet or 6 meters tall when on all fours. If their bodies were redesigned so they walked on their hind legs, and their front limbs became arms, and their overall weight greatly reduced, such creatures could reach very tall heights.

And on a low gravity planet which has a high enough escape velocity to retain a dense atmosphere, the lower gravity would help with some of hte problems with height, and the tallest bipeds might be considerably taller than the tallest possible on Earth.

Added 01-30-2022

I have suggested ways to possible create very large, tall, and heavy bipedal beings. So very old orks could have those body designs and survive to be very large if young orks also have those body designs. If only a few orks live long enough to need those body designs to survive, it would be improbable for the ork species to evolve such body shapes.

If only very old and very large orks get to reproduce, then the body plan of those very big orks would be the body plan of their species, even if it was not so helpful for young and small orks.

Unless, or course, the shape of an ork body changes over time. Most mammals change theri proportions a lot between birth and cessation of growth. Which is why humans can recognize baby mammals a lot of the time. They look infantile.

And even though most mammals have rather short gestation periods and many newborn mammals can already walk, the larger and more intelligent mammals tend to have much longer gestation periods, and even then their babies are less developed compared to adults.

Since your orks or Diremen are intelligent beings, there may be as much difference between their newborn babies and their final life stages as there is in humans, or even more so. Thus the proportions of Diremen will not only change as they grow from babies to adults, but also change after adulthood as they continue to grow.

This changing of body proportions might enable theoldsters to grow much more than if they kept the adult body plan and proportions unchanged as they grew.