Two thoughts:
1) Gukesh took Ding into the deep water the entire time. Few people realize how draining chess is, especially at that level for this time control. It's beyond gruelling. Only programming is more difficult ;-)
2) Gukesh had an extraordinary advantage. His mental health and resilience over the course of the match were a testament to it. And, then, his graciousness, thankfulness, and humble joy demonstrated the Way. It was That which Gukesh first thanked in his post-match interview with GM Mo. It was how he first began each game.
And That was the difference. That said, being 18 didn't hurt either :-)