Take a look at what the President tweeted about his impression of Kim's appearance and health when they met at the Korean DMZ on June 30 and contrast that with what Fox News Anchor, Tucker Carlson, reported in the following video.
Assuming Tucker Carlson's version is accurate wherein he describes Chairman Kim's ill-health (unlike the President, he has nothing to gain by lying about it), I would imagine that Kim depends greatly on his military leaders for support in order to remain in power...for health reasons, safety and security reasons, economic reasons, political reasons, and in order to maximize his priorities of securing North Korea's power as a nuclear powerhouse.
Without that important and immense military support system in place, and as long as they remain loyal to Kim, I believe his future would be very fragile and precarious because of his poor health. For that reason, I cannot foresee an agreement ever being reached between Kim Jong Un and President Trump to completely and verifiably denuclearize, because Trump is not just dealing with Kim, he is also dealing with all of Kim's military leaders/advisers...who are, essentially, propping him up, for the time-being. To create prosperity for the citizens of North Korea would undermine their absolute power over them -- and over Kim -- and would take away their nuclear power and leverage over the rest of the world.
If Kim were of robust health, I'd have a different opinion in this regard...he'd have absolute autonomy to make such a deal with the U.S. However, with so many hard-line military players involved (who are necessary for Kim's survival), the deck is stacked against such a deal ever being struck, with Kim Jong Un at the helm.
So, President Trump is only biding his time with Chairman Kim, using flattery as an interim appeasement tool -- sprinkled with another summit or two and more photo ops, that Kim can use to prop up his image with the North Koreans and the rest of the world -- until such time as he is no longer the U.S. President...and, no doubt, those rose glasses will stay firmly on until then.
In the meantime, I hope the President will not back-track on his maximum pressure campaign against North Korea and will, instead, begin to enforce the rules of that campaign on those countries that are, reportedly, breaking the sanctions that they originally supported at the U.N. (e.g., Russia and China, etc.).
* UPDATE July 26...
It looks like international sanctions against North Korea are working...If Chairman Kim wants to save his people from starvation, he will have to make major concessions soon, especially when it also begins to impact his military personnel...