My experience
Cranky CJ,
I tend to think your son won't have any trouble with it, especially since he can shoot your 12 gauge. My son is 11, and he can shoot my 25-06 ok. After about 8-10 rounds he's ready for a break, but he outshot me with it this summer and hunted with it this fall (we didn't see anything, unfortunately).
I have a stockpile of 115gr Nosler Partition bullets that I reload for it. Shot my first buck with that load, at about 80 yards, and hit him in the spine--looked like about 2-3 vertebrae ceased to exist...they were just gone.
There are other good loads too, and the Barnes bullets look very promising, though I haven't tried them yet. The beauty of the 25-06 is that you can load light bullets, like 75-80 grains, for varmints, and load the heavier bullets for game up to caribou. Some people take cow elk with it, but I'd be pretty nervous about doing that myself. Shot placement would have to be about perfect, and I'd have to be using a top-notch bullet before I'd consider it.
One other thought--if you can bear it, it might be a good idea to cut the stock down to fit your son. I got an aftermarket stock and cut it down, because I couldn't bring myself to cut the walnut on a pre-64 model 70.
If you go that route, keep in mind you probably won't need to cut much--I cut about 1.25 inches, and that was plenty for an 11-yr-old. Having a stock that fits made a world of difference for my son, and might help yours too. (Remember, you can always cut a bit more off...but ya can't put it back on.
)
Good luck!!
frayluisfan