When I picked up Tinkering I around level 4, the first quest I got was to sustain 15s of tinkering on a single tool. I have yet to break a tool that badly, and I'm level 11... but when I got a second Tinkering quest, it was to repair three tools, full stop.
The second quest makes more sense if it's the first one, since everyone has three tools in need of a little work after some digging, mining, and watering. By making "repair three tools" the first quest, you'd be providing an immediate hit of reward and satisfaction for the newbie tinker, instead of "...how do I break a tool that badly? How much wear will it have to take before I get a full 15s' tinker?"