I personally do not believe in ideal height at different ages as it can differ. Wait for atleast 6 to 8 months feed you dog a good balanced packaged diet and give suppliments as per the vet and all will be fine. Do not get tension thinking your dog is too small or should be bigger etc. Just enjoy it and start training and do not allow it to jump on you or on your bed etc. Basic obedience training you should be concentrating on.