Am I the only one who felt kind of uncomfortable about the fact that her character was 19 and his character was like over 30 (I mean like the time where he stopped aging were at his 30s)

I kept feeling that a 30+ year old were in love with a 19 year old high school girl D; 

Idk.. maybe I'm the only one

Either way, I haven't finished the series so don't spoil anything please haha

You're not the only one :/ I really can't understand why they made her a high school student. How childish she acts sometimes doesn't help either...
This is why I wasn't interested in that couple at all (or more on a friendship level). Sunny & Grim Reaper are much cuter anyway.
Yeah, I kind of agree with you, too. Age range didn't bother me at all but the thing that they are not feels like a "couple" is right, I think. Even if I love whole cast, the relationships are a bit... how should I say? Strange or inconsistent... I don't know.
I am one of those who personally wasn't really bothered about it :x.. If you think about it Kim Shin is like 900++ years old.. So can't really do anything with the age difference... and not sure where u'r up to at goblin.. maybe when you're finished it you may kind of understand why she started off so young? 

It kinda goes with the story line if you think about it.. and i don't know where you are up too sooo Lol!
@FiPancake:
But Kim Shin was a certain age when he died & became immortal/stopped aging, and that age has definitely quite a gap with Eun Tak's age. 
You can also look at the actors playing the characters. They're 37 & 25. Gong Yoo (Kim Shin) looks definitely late thirties, but Go Eun (Eun Tak) could easily play the teenage/high school years as well. This makes the age gap quite salient even if story-wise 10 years more or less don't really make a difference.

@Nor:
Hmm let me try to explain my train of thought..... 

*Highlight since there is spoilers*

In the drama Eun Tak is a missing soul and as what the grim reaper says she will meet a Grim Reaper at the ages 19, 29, 39 ect as 9 is the closest incomplete number to 10. 

So if Eun Tak started out as a university student at 20+ she wouldn't meet a grim reaper and possibly the story will not unravel until she is 29..  
After 9 years after Kim Shin disappears she would meet Kim Shin again at the age 39 which would make her older than Kim Shin (assuming that kim shin stopped aging before 39) and we wouldn't really be able to enjoy her transition from a university student to a PD (Achieving her dreams..). Perhaps the author didn't want Eun Tak to meet him at the age of 29 as its already 1/4 of her life past and in the drama she does pass away young so she could meet Kim Shin in her next life and live a longer life. 

Not sure if i was clear.. but because of that i felt that her being a high school student really didn't bother me much... :X
I think that Sunny and the Grim Reaper are cuter. I love the whole cast, don't get me wrong, but I think that, for me, her childish character sometimes irritates me a lil' bit.