In the monster manual, it states that if you get it as a hatchling, you can raise a wyvern much easier but how long would that take? It doesn't state how old they can live and how long it takes an egg to hatch, so is there any obscure rule or something on the age of Wyverns? It seems like a pretty big oversight to mention you should get hatchlings but not mention how long it takes for them to mature. I'm not really using it, but I was just wondering if there was something somewhere on this topic.
This is one of those things on which D&D bows to the DM's authority over their world. D&D has provided the creature, but not all the details of its life cycle, ecology, mating habits, regional variations, history, origin, etc. ad nauseum. Different editions have given more or less detail on these aspects of creatures, and this is the level of detail 5e has settled on.
So, in a phrase, "ask your DM," since it will vary according to what the DM wants for their setting. In one setting wyverns might be like reptilian mayflies who live only a year and die every winter, while in another setting they can live thousands of years, and in a third setting they have a lifespan similar to cats, etc.
First, a Wyvern has dragonsblood but are not what the MM deems a true dragon. Be that as it may, it seems true dragons live to 800 years old or more. Let's say we cut that in half for a Wyvern and make it 400 (Speculation). Now you have a measurement of time.
- Wyrmling: 5 years old or less
- Young: 6 - 100 years
- Adult: 101-800 Years
- Ancient: 801 +
Second, as to the finding of an egg, hatching and raising of a hatchling Wyvern, and then taming it. The MM says it is a Difficult and Deadly Challenge (Which actually gives you challenge/Difficulty ratings for attempting to do exactly that using dice roll...which you would use multiple dice roll over the course of weeks/months to maintain a success rate.)
PHB pg 187:
Downtime Activies: : "...Between adventures, the DM might ask you what your character is doing during his/her downtime. Periods vary in duration, but each downtime activity requires a certain number of days to complete before you gain any benefit, and at least 8 hours of each day must be spent on the chosen activity. The days do not need to be consecutive..."
It goes on to say that if there is something you'd like your character to be doing (Such as raising a Wyvern egg.) you may discuss it with your DM. He or She will tell you what an appropriate amount of time to be spending doing said activity would be. These lengths of time are extensive however. Training in the use of a set of tools takes 250 days. Smithing a suit of armor is 5GP per day of smithing towards the market price of any craftable metallic object. (A 1,500 suit of plate armor would take 300 days: 1500 / 5 = 300) . Hatching a Wyvern egg and the subsequent training/raising of the baby Wyvern into a creature of a proper companion size would take equal time.
The above is, of course, my interpretation and decision on how I would run that sort of downtime activity. I would say to expect to spend a lot of time caring for a Wyvern egg and probably a year (365 days) raising it into a creature that can begin to learn orders and commands and not just want to eat meat and sleep....
Most animals in the wild grow the most in their youth. It's a survival trait of almost all life to grow as fast as you can to 1) survive and 2) produce offspring.
Those two things (survive and make more) are the prime directives of all life.
Using the dragon table kindly provided in another answer and understanding that a wyvern is not really a true dragon but a smaller cousin and combining that with an extrapolation of riding animals in general (horses, camels, oxen, elephants, etc). Where they can be trained and ridden as young as 1 to 2 years old. It would be easy to speculate that a wyvern could also be trained and ridden while young. Therefore I place the age of rideable size at 2 1/2 to 5 years years based on the dragon age table saying young age begins at 5 and that wyvern a are smaller cousins of dragons and that smaller varieties of life forms mature and age faster than larger varieties.
Let us confirm at least a few separate assumed truths in a fantasy setting.
a) Wyverns are beasts, but aren't magical beasts.
b) Wyverns are reptiles, but what type of reptiles is the question.
1)Extant archosaurs (we'll assume Wyverns are) are in the real world, and phylo-genetically they are the descendants of dinosaurs which are represented by birds and crocodilians.
c) Accepting above , we must make th decision if wyverns are more like crocodilians for their maturation rates, or more like that of birds.
1) Either way, the larger a verterbrate organisms adult size is, the longer their maturation rate.
d) If we assume that wyverns are more avian than croc, then their maturation rate would increase quite a bit.
1) The maturation rate of the largest crocodilians is years. In fact longer than humans. Even with an optimal environment with limitless caloric intake.
2) Wild ostriches have a maturation rate close to one year, whereas domestic ostriches are closer to half a year.
e) Taking all this into account, one might assume that wild wyverns are more likely to mature at the rate of an enormous bird, but perhaps we should multiply that growth for size, and perhaps slow it down a bit towards the crocodilian side of things.
Given all of the above we can say that wyvern eggs probably hatch, under optimal conditions, quite quickly. As do both reptile and bird eggs. Lets say two months at most.
Given a wild environment, a wyvern likely won't start flying on its own for about a year. AT which time they might start bravely leaving the nest, and becoming independent by year two..at which point they aren't fully grown, and are basically subadults, but like crocodilians, are capable of surviving on their own.
Now, lets assume that their's a market for domesticated wyverns. Entrepreneurial thieves that have made a living stealing wyvern eggs until they could find a tameable mating pair.
So , a wyvern probably could be a rideable mount for a human until it's around at least 7 years old. Unless it was a domesticated wyvern, which might be 5ish.
Needless to say. You're better off spening the 50000 gps to buy an adult that's been trained already.