I don't really have a number. I just went with the observation of him standing next to Marcus Tennis (host) and comparing that with other interviewees. He just doesn't look that tall.
Strangely, a lot of our very best juniors seem short compared to the rest of the world. Kozlov, wiersholm, mcdonald, rubin all seem pretty short. Even Fratangelo doesn't look that big or tall for his age. From pictures I've seen of Spencer Papa he seems like he's got a pretty good athletic build for 17. Not skinny and short like the rest of them.
I don't think it is strange that our juniors are shorter than those from other countries because most of the athletic/tall kids are usually recruited by other sports (football, basketball, baseball, etc.).
Papa does seem to have a good build for a 16 yrs old (doesn't turn 17 until October). Halebian, Kwiatkowski, Donaldson, Escobedo, Corinteli, and Mmoh are also tall (they all seem to have similar gamestyle as well). I think there is a correlation between height and gamestyle. Tall players tend to be ballbasher while short players are forced to play smarter (through variety, court-positioning, point construction etc.) b/c of their lack of power (Kozlov and Wiersholm are good examples).