# How do you determine age of a humanoid species comparative to humans?

In my book, there are humans and there are Shaye, a humanoid species that are a little like harpies but with other features that distinguish them. Comparitively to humans, they live far longer so the development of age is viewed a little differently. My problem is, I don't know in what way it should be different.
Here are the options:

1. Shaye develop slower both physically and mentally. This would mean that whilst a human is, say, 2 years old, a Shaye of the same physical and mental development would have been alive for 4 years (or something like that). Once fully developed (let's say 35 human years) they both stop developing but Shaye live until (for example) 200.
2. The development as a Shaye child is the same pace as a human but as they grow older, it starts to slow down. For example, up until the 18 years old, both humans and Shaye are at the same stage of development both physically and mentally. After that, the Shaye develop slower but live longer.
3. They both develop physically and mentally at the same rate but Shaye just so happen to live for longer.

In my head, my Shaye character is at the mental and physical age of a 17 year old but has been alive a lot longer. This would have to mean the development rate was either option 1 or 2. However, I'm bad at maths and other problem solving situations so I don't know how I would make this work. It also means that I don't have a good reference of time or how old any other Shaye would be and unfortunately this puts a stop to the plot planning until I can figure it out.

What would be my best option and is there a visual way of portraying it so I can track it for other Shaye characters?

(All numbers I have used in points 1, 2 and 3 are purely place holders and can/should be changed to fit an accurate development rate).

• 4. They age faster reaching full emotional and physical maturity equivalent to human mid to late twenties within ten year then largely seem unaging to most casual human observers until their last twenty years after which they age rapidly until death .. this is an entirely story based choice, there's no problem to be solved or knowledge being sought here, it's just polling for a 'what do you like best' question ;p Commented Mar 9 at 0:34
• do they have feathers? maybe the young ones still have their juvenile plumage just like we have our wisdom tooth. Commented Mar 9 at 4:40
• @user6760 that part of their physique at least is something I'd expect to reach full maturity very early, big bulky wings that don't work for years (or for even decades) are heavily contraindicated as a waste of space and resources for an organism evolutionary wise > either they can use them within the first couple of years (or sooner) or (as babies or toddlers wandering off too easily and getting themselves killed is also bad evolution-wise) those limbs (the wings) only start growing beyond the smallest of vestigial nubs much later on in their development is what I'd go for there. Commented Mar 9 at 15:00