He may quickly out grow it physically and a scotty is too nice to be cutting down in my opinion.  I don't think that the weight would be too greatly affected.

Cutting it down will impact the swing weight and he may not like the feel after that point.  Although, the worst that can happen is you have to send it back to SC to have it re-shafted.

Have a Pro cut it when HE fits it to your son, you're going to throw the swing weight wayyy off, good luck!

The most important part of a putter fitting is length and lie.

I bought a Monterey 35" inch and had it cut down to 32.5" so that I could have the lighter swing weight that I prefer. I could have gone with the 33" and cut it down.5" but then it would be heavier than I would like, due to the different stock weights.

Bob,

I'm not a certified fitter, but this is just my opinion.  Scotties are wonderful putters and to  me having it close to integrity would be how they we designed for optimum results.  I think, cutting, bending ant tweaking should be left to the pros/scratch players who aren't growing anymore height wise . 

Your son being 13 is in the prime time for growth spurts and should be growing instantaneously.  Within a year or two he could be growing 3-5 inches, thus outgrowing the cut.  To me he should be able to choke up or lean the shaft on his forward arm for a few months before growing into it.

Again, this is just an opinion, the choice is yours.

Good Luck 

Put on a counter-balance grip and have him choke down for a while.  Once he grows and no longer needs to choke down, then switch back to a standard grip.

I would have no issues cutting a Scotty down for my son (and I will when he gets a little older).  But if he's 13, I would think twice about it.  How much were you planning to cut off?  Anything more than an inch (maybe two) and he'll probably outgrow it by next season.  At this point, if I were you, I would maybe cut it down to 34 inches.  It will affect the swing weight some, but that small of a cut shouldn't be too noticeable.  Hopefully it would be short enough that he could use and grow into it, but it's also long enough that he may never need to change the shaft.  I'm 6'5" and have played with a 34" putter for many years.

The other alternative to having it cut down is to pull the current shaft and have a shorter shaft installed so you can just replace the original shaft when he outgrows the cut-down version.