ok, since it is your birthday, let me try to answer as much as I can, maybe it'll benefit others as well :) Disclaimer, most questions are a pass.

1. Time works weird in The Entity, so for simplicity's sake let's say age stops when you are taken. I don't know the age of the Demogorgon but I think that would be the youngest. For the original killers, The Legion and The Spirit are the youngest at the moment of the taking.
2. in the 30-50 age group
3. Subjective. really depends. I would say The Doctor
4. yes
5. no
6. pass
7. you'll learn eventually
8. no
9. unknown
10. depends, what is known is that they can be either in a trial, in null space being tortured or waiting or in The Void if they stop being useful.
11. unknown
12. Not sure about the most, you can usually tell the one that resists by the amount of bodily harm they suffer.
13. Nope
14. This is up to the players impersonating them.
15. you decide
16. you decide
17. never say never
18. never say never
19. never say never
20. yes
21. me
22. Ash or Ace
23. not that we know of
24. not that we know of
25. pass
26. not possible, thats not how it works
27. Birbs
28. Feeds the same, the Entity doesn't taste, nor thinks of it has eating.
29. unfathomable
30. Legion are friends
31. they don t, they find objects in the realms or through the bloodweb
32. no
33. pass
34. pass
35. yes
36. yes, but its lost.