65lb is NOT small for an adult male boxer. It is correct!!! This is not a breed that is supposed to be 80-90lb, and most of those that do weigh that much are actually fat (however much their owners protest that it's "all muscle").
Considering that your dog is still only an adolescent, I really don't think you should be worrying too much about him being in any way small as the likelihood is that he'll put on a bit more weight in muscle over the next 6mths to a year. He'll be finished filling out by 2-3 years old (anything gained after that time is probably middle-aged spread (fat)). Better to wait until you see the "finished product" before worrying about him being small (though as above, he is NOT small - the correct weight for an
adult male boxer in the middle of the height range for this breed is about 64lb, and your dog isn't even an adult yet).
PS: Your adolescent weighs more than Henri, my 7 year old - and Henri is certainly not undersized
