I seem to be in the minority here for having noticed him during ARR. He was annoying at the begining of the CT arc, but then he seemed interesting with his seeking the mystery of the tower, and I was worried about him having those painful-looking flashes of memory and what would happen to him in the end. And the conclusion seemed like a setup for future story development.
In any case, his appeal in Shadowbringers isn't anything to do with him "looking fancier" but his personality - however you want to interpret his exact feelings towards your character, they're clearly strong: everything from his grand plan to save your life to the way he fidgets nervously as he waits for you to answer the door, shows that he cares deeply about you.
That's what makes him an appealing character to me. I'm not 'in love' with him (though as I've discussed elsewhere, I think my character might be) but I feel... affection? appreciation? to him for all that he went through for our sake.
Not knowing what artwork you're talking about... are you sure it's not just the person's art style?
For me personally (though I haven't done any FFXIV art specifically) any characters I draw tend to come out younger and 'cuter' looking than they're supposed to be - it's nothing to do with intent, it's just how I draw, and I'm not trying to portray them as younger than they actually are. I'm just bad at making them look mature.
It's also probably about whether you focus on the image itself or connect it back to the character as they actually are in the game. If someone's art style made the characters "look like" children, I wouldn't assume the art was portraying them as children - I'd just think of the characters. Like... chibi art, or even games that use that kind of style to represent their obviously-adult characters in a way that doesn't look like an adult at all.
I think spoiler tags are a lost cause at this point in the discussion...
And actually we know he's at least somewhere around 120 in Shadowbringers, not counting his time in stasis - he's 24 in CT, the Flood occurred a hundred years ago, and he arrived on the First not long after that.
The "life expectancy of 50 years" thing came up in another discussion recently, and apparently that's more to do with their living in harsh conditions as hunter-gatherers, and all the races can live a normal human lifespan.
I absolutely agree that the G'raha Tia currently sleeping in the tower is not the same person as the Exarch - but he's not quite the annoying guy who stole our aethersand and made us run all over the Twelveswood to get it back, either. He went through some character development and introspection over that original story arc, and "awakened to his destiny" as the keeper of Allag's secrets. By the time those doors close, he's a more mature person than the one we met at the start.
I still don't think we're going to be getting him out of the tower now though. As I've said elsewhere, the optional-ness of the CT storyline means that he might not even be in there yet, which is a bit of a complication for bringing him into the MSQ. The time-travel plot is basically necessary to get around that issue.
You may want to re-read Fynlar's post, which I'm pretty sure is the only time autism was brought up in the entire thread:
That said... it's not necessarily an autism thing to not get attached to fictional characters either. Being a long-diagnosed Aspie myself, fiction was probably a big help to younger-me learning to understand how other people are feeling. Despite the stereotype of lacking empathy, that's not the case for me - but understanding how to process and respond to it is another issue entirely.