That's the thing... Age is highly, highly related the curability. The Lidcombe program is generally used for kids this young. It isn't perfect, but there are cases of kids this young getting treatment and no longer having a stutter. Lidcombe is from New Zealand, which happens to pour lots and lots of money into research, so it is also very well studied with at least a couple of randomized controlled trials. If you wait, then yes, it could resolve on its own, or become a lifelong issue. Lidcombe is not overly burdensome either... Should take a year or less.