Seems to me all choices would still be given serious consideration if the OP did a little investigation into resistance training to up his strength and minimize the fatigue factor. Cheers to all.
I have tried 3 types but I always end up using my Think Tank Sling. It has the advantage of wrapping around your waist while riding so nothing hanging down your chest loosely bouncing about and when walking you can wear it as a one side shoulder sling for easy access. It holds extra batteries, etc. plus 2 lenses for my Sony A6000 series camera.
I recall listening to an ophthalmologist giving interesting facts about the human eye. One factoid I kept was the eye has the equivalent of 48 megapixels. So I guess taking the first digital crop down to 50 will still loose nothing to our naked eyes viewing at any distance.
Not trying to be the grump on here but what's so bad about just saying I'd prefer you wait until you're stronger / older? Teaching kids that somethings are expensive and need to be dealt with accordingly.