Your character is referred to as "young" by the game text and called "kid" by Varric. One of the romance options is a man in his 50s. It's handled carefully though. He's even reluctant to enter the romance at first specifically because of the age gap.
As seen in a trailer, literally one of the main characters is a "Dragon hunter" and is seen fighting a furious animalistic dragon. So yeah, there DEFINITELY will be dragon killing.
EDIT: Yeah… The answer is obvious and totally not surprising since this whole franchise is basically about dragon killing and enslaving… smh
Yes, you can see dead Halla (deer-like animal) in one part of a map, and in another quest you set out corpses of deepstalkers (dinosaur/raptor) for bait for a dragon.
A good bit of blood, including a scene where a minor antagonist is bathing in it, and lots of gross gore-like things in the environment. Including things that look like intestines and boils/blisters.
Lots of enemies are shown to be "altered" in someway. Boils on their bodies, too many horns, things of that nature. A main antagonist's body is disproportionately long with too many arms + tentacles, and her eyes are replaces with fleshy masses as the game progresses.
Two major characters die, and these deaths are unavoidable.
(MAJOR SPOILERS) 1. A character is stabbed in the beginning of the game and appears to be fine and bandaged up in the next scene, but this is a ruse and he's actually dead. 2. In the endgame, you need to pick between Davrin and Harding to lead a mission. Whoever you pick will die.
A companion is kidnapped and held captive before you meet him, and his first quest is for you to rescue him. There are a few more instances of offscreen kidnapping throughout the game, or missions where you have to rescue people who have been taken captive.
One of the companions has moments where she stops talking mid sentence or stares into space/seems to be "not there", which could be reminiscent of dissociation.
Yes - kind of. There is an underwater area that is protected by magic, so you can walk around and breathe. But the barrier is invisible so you can see sea creatures/coral/water past it.
"Demons" is used in-universe as a term for malevolent spirits, they often represent a sin (envy, wrath) or negative emotion of some kind. A party member is possessed by one of these demons.
LOTS. Fictional religion. But there are plenty of conversations about questioning faith/being very shaken about not knowing what to believe any more, religious discrimination, and different gods intentions.