[Newcastle]

I agree with what's been said here - the testicles may still come down, they will still be producing sperm, and if they remain undescended they are 13.6 times more likely to become cancerous.  (This does not mean you need to neuter him now, or right at six months; there are reasons to delay neutering, and the treatment for testicular cancer is neutering in any case - it doesn't usually spread - but if they don't descend, I personally would recommend neutering after 18 months or two years of age.)  

I mentioned health risks for spay/neuter that are generally ignored; here's an article that is exceptionally well-researched and balanced, giving both the benefits and risks of spay/neuter:
http://www.naiaonline.org/pdfs/LongTerm ... InDogs.pdf