I used this with both of mine, with varying success, like Joules says its how well you stick to the training.
With Ben (who was 6 when we started out of desperation as he kept running off to eat things, chase things or roll) we bought as long-line, whistle and went right back to basics, OH and I agreed to be consistent in choice of words, how we rewarded etc. and we put in lots of training every day, with the most delicious treats we could find. Ben is very food motivated anyway, and the training was superb he actually got it very quickly, but we kept practising for another couple of weeks increasing the distractions. I would argue he is 100% as in 6 years he has never failed to come back to the whistle once, from anything
. He also really changed as when we were walking he stopped roaming too far away and kept looking at us so we could do verbal recalls as well.
Harry is a different matter
I always argue that he was allowed to chase before he came to us, so already had a well developed chase instinct. He also is not as food motivated as Ben. But with all honesty I know we never put in the same work either. For the first year he was with us he was too traumatised to do anything, he couldn't even sit on command without quivering in fear
But we haven't put in the same intensive training and it shows. He is fairly sheep proof (not 100%) but pheasants and rabbits are another matter !
I would guess that at 12 weeks is a great time to start. If I have another pup at some stage, I would just not ever let him think he can get away with not returning to the recall, and would use a long line to make sure if I whistle he comes back
I think the problem comes when you whistle and they don't come back and they are too far away for you to get to. So small spaces to start, good treats, and use a longline to reel him in
and gradually increase the distractions. Good luck I am sure Alfie will do well