I'm not an expert, but I too have a 7 month old Norwegian elkhound. Mine weighs 20.5 kgs and is not overweight, so I'd say yours is probably at a good weight for his age. Check out my puppy's pictures at http://www.doggyspace.com/profile/27351 and see if you think yours is much larger than mine. I think that my puppy tends to be on the lean side for his breed.
MY SON ELKHOUND IS 6 MON THS TODAY , HE WEIGHS 42 LBS , NOTOVER WEIGHT