Lots of good options mentioned and he's 2 more!
The Head Framewall is a fantastic light weight twin tip with a 84 waist with tip /tail rocker for catch free spinning. It has a sidewall that extends 360 degrees around the ski giving it more stability and making it chip proof. Works in the park and all over the mountain. I had a pair in 181cm for similar use to your son. Asogear.com has a pair in his size(171cm) along with the great lightweight Tyrolia Attack 13 bindings for $249.99 for the package! Amazing deal.
Another fantastic twin tip with tons of "kid street cred" would be the Armada El Rey or its new name the Armada AVR 84.(The 2015 or 2016 El Rey has beefier edges than the AVR 84, so first pick would be the El Rey). Full Camber with no rocker but not a "catchy" ski with great hard snow grip and still playful. It's around 84 at the waist as well in the 171cm length. Full cap construction which is usual very soft flexing but this ski not at all. Great flex and you get great durable and lack of chipping because of the cap construction. Amazon has the 171cm El Rey on for $359.99 for the pair and lots of places with the Tyrolia Attack 13 binding for $120 to go with them.
Good luck with the search!
The Head Framewall is a fantastic light weight twin tip with a 84 waist with tip /tail rocker for catch free spinning. It has a sidewall that extends 360 degrees around the ski giving it more stability and making it chip proof. Works in the park and all over the mountain. I had a pair in 181cm for similar use to your son. Asogear.com has a pair in his size(171cm) along with the great lightweight Tyrolia Attack 13 bindings for $249.99 for the package! Amazing deal.
Another fantastic twin tip with tons of "kid street cred" would be the Armada El Rey or its new name the Armada AVR 84.(The 2015 or 2016 El Rey has beefier edges than the AVR 84, so first pick would be the El Rey). Full Camber with no rocker but not a "catchy" ski with great hard snow grip and still playful. It's around 84 at the waist as well in the 171cm length. Full cap construction which is usual very soft flexing but this ski not at all. Great flex and you get great durable and lack of chipping because of the cap construction. Amazon has the 171cm El Rey on for $359.99 for the pair and lots of places with the Tyrolia Attack 13 binding for $120 to go with them.
Good luck with the search!