I think that load would get the job done just fine, but personally I'd use a lighter bullet if you can. Recoil depends on powder charge and bullet weight both, and a 300 grain bullet is probably overkill for a youth load. My bullet choices in order for a youth/light recoiling load would be:
1. 40 cal 200 grain XTP (with a .50/.40 sabot) & 60 grains T7.
A guy on another forum uses this bullet with 65 grains T7 with great success on deer and javelina. I've killed 3 deer with this bullet (using 80 - 100 grains T7 at various ranges), and I can say with confidence that it expands and kills well at low & high velocities both.
2. .429 240 grain XTP (or .45 250 XTP) The other guys in my hunting party use both of these and have had great success with loads ranging from 70 - 90 grains T7. I'm sure either would work just fine with 60 grains of T7 for close range shots as well.
3. If you want to stick with the SST/Shockwave, I would use either the 250 grainer or the 200 grain Shockwave- less weight = less recoil, plus these should expand a bit better at low velocities than the 300 grainer.
Hope this helps!