Totally. Just like Volkanovski.
You hit the nail on the head, I think. Fighters really do fall off a cliff once they reach whatever age it is that they're too old to fight.
Maybe it's because MMA is so multifaceted - when your physicality starts diminishing there are a million different ways to accomodate and hang on, to slow your descent, until you reach a point where even these workarounds arent effective anymore and then bam, you suddenly just can't do it any more.
The Jones situation is a very good one to illustrate this. On the one hand, he looked amazing in his last fight by demolishing a great fighter in Gane. On the other hand, Gane isn't anywhere close to the wrestler Jones is, so maybe it was just a matter of that - Jones's wrestling was FAR superior, and he was somewhat lucky to get the takedown and dominant position he did.
Looking at it another way, Jon has fought exactly once in more than 4 years in a fight that only lasted 2 minutes. Add to that he's had a long career already, has recently been badly injured and is fighting at a new weightclass - there's a good chance he's well over the cliff today.