Hi Confession matey,
I know full well how difficult it is broaching this subject with your loved ones when you feel they themselves are in a delicate stage of their own lives. My mother was particularly fragile when I could no longer avoid giving a straight answer to her on the fact that I was resolute that I would never return to the org. I think there are no real ideal times when it comes to this sort of thing, there are probably less ideal times, but it doesn't sound that apart from your parents being slightly older that there is much reason to hold on and wait.
The problem with holding off any longer of course is that you are left in a state of limbo, and can't fully move on with your life. We're too old to be fearing the wrath of our parents. While it is to be highly commended that your hesitation is because of the love for your parents, there is also the possibility that you are not yourself ready for the full scale shunning that might result. I don't know if you can ever really be ready for that, doesn't matter how hold you are.
I know it is easy to say this, but you are no responsible for sheltering your parents from reality and the world. They are well and truly grown up, and you don't owe them anything other than love and support. It might sound selfish, but in the end you are the only one looking out for you. While they might not fully allow themselves to understand your motives, you can take heart in the fact that at the heart of things all that the people who love from us want is for us to be happy, true and fulfilled. Despite that there selfish desire to have you in the org might take them over for a while, they will learn to cope with it, and move on.
You can't protect these people from the truth about life and your reality, afterall that very notion is what caused you to make this stand in the first place. So, don't for a moment feel guilty, or allow them to put guilt on you. You know you have the moral highground, even if they are so blind as to not be able to see it. You can't protect them, that's not your job.
Wish you all the best. Take care, Frog xx