Tell him you did the best you knew how to do at the time, when you knew better, you did better. How can he expect better than that?
It is a shame he didn't get a chance to go for his dream, but it doesn't mean that's the only dream he can ever have. As long as he is playing "what if", instead of being born to a JW family, what if: He was born blind or he was born in a poor, third world country or he was autistic or he had cancer.
I wasted most of my life on this stupid cult, I was forty five and had health problems by the time I got out, but I don't dwell on that, I just am thankful I didn't waste any more time than that, and I enjoy the life I have right now.
Attitude is everything.