At 250, look in the upper 160 range; something around 1670 through 172 would be perfect. A stiff board is going to be better as it will retain it`s camber with a heavier rider better. If you do a lot of Powder riding, consider a mid wide to a full wide. His boot size does not require a wide board, but the extra CM of waist width will come in very handy for him when free riding pow. A board I can`t speak highly enough about and would also be ideal for him is the Atomic Radon in a 169. I have one as my Pow board and while it is huge for my weight, it still handles groomers, ice and even park very well for me. The only time I notice it`s length being noticable is in tight trees; I have to take more open lines with it.
I just googled it, thats a sweeet board.... not sure he will be that lucky for his first one!