Alfie is 16 weeks and has learnt to "give". I taught him to sit, stay and go (fetch the ball) and when he returns to give. This worked with loads of treats and really praising him and didn't take long at all... I do about 15 minutes a day. Whenever he has anything in his mouth and I say "give" he does! Even today I could hear something rattling in his mouth. I said "give" a few times and out it popped, my daughters plastic plectrum, she was horrified but I was so pleased he did as he was told and spat it out
This may work for you, once they learn the basic commands like sit, stay, go, give, it makes life a bit easier. Now all I need to do is stop the play biting!