6 months of training?

[KAI'S MOM]

Our new male boxer is 4 months old. Very smart (aren't they all). He's great with peeing outside, haven't had an accident in about a month now even sleeps through the night! But we can't seem to nix the biting (teething) stage. Funny also is that he will listen and play gentle with everyone in the family (me, hubby and 5 yr old) but will not stop using my 8 yr old as his chew toy. Tried all the methods I've read about here. Yelp, walk away, leave him alone for 5 minutes, give him something else to chew on but nothing. So a dog trainer we went to see says he can help us with that. Training is 2 days a week (1/2 hr/day) for 6 months. Starting now at 4 months.
Question: Is he too young? The breeder says that he will soon go through his teenage yrs and will forget everything. Also is 6 months too long a training course? We'll try anything but I think this maybe too early or too intense?

 

[Rlr.Giraffe]

Willis couldn't stop biting our hands until he was about 6 months... just couldn't get the idea that he wasn't supposed to do that no matter what we tried!!!!! Then, he just stopped. We were really consistent about "no biting" and ignoring and then one day it just clicked I guess... he mouths us now, but never uses teeth. We don't mind that! At 4 months, your pup is probably teething and biting probably feels like the natural thing to do... I think I'd wait for a bit to see whether it cuts out after he's got all of his new teeth (but be consistent with training in the meantime).

Six months does sound like a long time... I'd investigate other trainers .