If you are looking for a kite to do mixed duty as a trainer/riding kite for a 115lb rider, the 3m Peak 4 is what I would put him on. It will give him something to learn on that will be fun, forgiving and nearly indestructible but can still easily be used for riding in moderate winds when surface conditions and wind conditions allow.
Eventually as he grows and his skillset grows, he'll want more power and the 3m will be relegated to his high wind option.
The 3m is our go to for beginner riders on the 90 to 120 lb range.
It is a kite that responds well to line length for power management. 10 years ago doing lessons in anything over 20kts was generally a challenge. Now with the performance available in the Peak 4, with the right line length, lessons in 30kts are actually fun.
It's a great all rounder.
Side note, NPWs can't come anywhere near the upwind that a Peak or other current single skin can manage. Which will help considerably.
A few things to consider before making a choice would be what would the average wind range be? Is he on skis or a board? What are the dimensions of the ski/board? What would be the most common surface condition and terrain type?
What is on your feet is at least as important as what you put in the air.
In regard to modding the old Turbo bar. The Peak, Shaman or Explore (Ozone single skin) all can be used with a 5th line safety or an front line safety. The Turbo uses the old top hat safety found on early Ozone and HQs. It may work to some extent but not ideally.