The turtles fit, size-wise. However, he's not a believer....thinks that it's "easier" in split fins. I'm curious if a more neutrally buoyant fin would work better for him, or if he just needs a couple more dives in them to get used to how they feel....
He'll have to decide what he wants as I can't do it for him.
If he's not frog kicking and he's used to splits, I can pretty much guarantee he's going to hate paddle fins, especially Jets, Turtles and most of all, SlipStreams. They're just not as easy with a flutter kick.
Get him frog kicking, though, and he'll move away from the splits pretty fast.