The reason neither Jon or Chris's age-up landed is simple it's a coming of age story without the actual "Coming of" part, the period that should inform who they are now is missing/doesn't exist and so writers have nothing to draw from and have no real idea who they're suppose to be now as adults just that there not their kid selves anymore resulting in some very generic and ill-defined characters.
There's a reason other mediums in general don't do this and if there's a time-skip it's the entire narrative that shifts not just one character outside of it.
If the novelty of kid Jon was something that suppose to wear off and I'm just wondering when's the novelty of Teen Jon suppose to wear in? 5 years now and I've never seen any discussion (outside his bisexuality) around this character in any great length that doesn't go back to his age-up in someway.
If it hasn't clicked by now I doubt it's ever going to which is fine with me because once DC stops pushing him as hard maybe they'll allow Conner and some of the other Supers to get some shine again.