If you're talking about just making things to solve a problem. Like designing or modifying a circuit or any kind of on the fly manipulation. I'd say somewhere in the neighborhood of middle school.
If you're talking about what is commonly referred to as being a "maker". Such as using an additive 3d printer or subtractive laser cutter, or traditional CNC mill. then about 2 years. Friend of mine bought and assembled an ultimaker, and I've designed and created a few pieces of unique "devices" with it. Gopro scuba mask mounts, retainer ring for a bag to take my slr out in the rain, adapter to mount my cell phone on a standard tripod etc.
There is a nice maker space about an hour away from me at USF, but I think it might be restricted to students of USF.
People who make constantly reference PLA as not being durable enough to use for anything other than a bona fide prototype. I've got a few pieces of PLA that are fairly well used and at least a year old now. I think it's an underrated material.
FWIW, you can put together an ultimaker for around $1000, and that's one of the best additive consumer grade 3d printers around. Fortunately, the plans for the thing are entirely open source so you could go to a maker space and make your own, or get one from ebay for next to nothing.
