My sympathies are with you...my girl got baptised at 14 and even though I was 'in' at the time I knew she wasn't ready and was making an emotional decision to try to fit in. Now she is leaving the religion we have to tread very carefully with a fade so she won't be df'd.
I would try to advise him the things we don't get told when we are baptised, his brain is not even fully developed yet, he is going to mature a lot over the next few years and may want to make different choices, the consequences if he gets baptised at this age are a lot worse than if he just waits it out until he is a bit older to make an informed and mature choice.
As for distracting him from the religion, I didn't try to talk TTATT with my daughter at all, knowing I would push her further in, but she had a lot of problems with friendships in the org, so I just started to let her spend more time with her schoolfriends and she naturally has moved towards them and away from the witnesses, so that now shes made her choice to leave of her own accord. She can't face the judgement of the jws looking at her with criticism because she is associating with 'worldly' ones and she says she can't support a group that wants to see all of her schoolfriends killed at armageddon.