Rescuing/Adopting young cats
When I rescued Grasshopper, she was just under three months old. She clung to me like velcro also. I concluded later on that it was a bonding process. She was my shadow all of her nearly 18 years, however the clinginess lightened up as she grew older.
I have just adopted Spencer, who is around four years old, and although in the short time we've been together, he has become attached, and is affectionate, he hasn't "velcro'd" me all the time like Grassopper did. I find the quality of affection to be the same, so my conclusion has been it was due to the age of the kitty when I entered his or her life.
Perhaps this is the case with Loki, especially considering how young he is - ? It's kind of like babies - as tiring as it is being up and down all night, you know those days of need and nurture will never come again, and you deal with them and treasure them. (Most of the time ;) !)