I've done 50-plus feet and lots between 35 and 50 feet. There are guys who have done much higher and more. Height matters less than the lead-in. If the take-off is smooth, who knows how high we can go. The young guys will push this more than we did, but they'll also find out, like we did, that a small mistake on anything over 30 feet can do a number on you.
Height is one element of waterfall-running difficulty.
The others are the complexity of the approach and how deep and clear the pool is below. You need to be confident about making your line, leave the top with the speed and angle that will discourage goofing up during the free fall, and have a plan for finishing the drop in the pool below. Be sure to have a safety plan. I have gone out of my way to run a waterfall once, and have run a few that are around 25 feet. I have also run many more drops which are as difficult and more vertical.