That used to be me - not rolling; jumping from the swing. Great fun up at the lake - climb onto the boathouse roof for a really big swing, then let go into the water. 'Till one day, I just couldn't let go - took a while before I could let go again.
Go back to basics with your student. If he is having trouble with standing rolls, go right back to kneeling rolls or if that's still
too intense, to ushiro-ukemi, or rolling practice. (Sitting, rolling to the back, back to sitting.) Backward rolls are easier to deal with for many; so work on them.
This is actually a brilliant chance to work on technique, so go slow and easy and work on the mechanics of the roll. Putting it into a technical frame may get his mind off "Floor coming!" and onto doing it properly IOW, his mind'll be busy enough not to deal with the fright. Soon, as youngsters will he'll be getting bored with your slow pace and start wanting to go full steam ahead again.