How sudden

My condolences on Bella. I know that it is heartbreaking losing a special pet. In time may you find peace, and remember all the good times with Bella, as I'm sure she gave you lots of them. Sending warm thoughts your way.
I have a 2yo yt and knew of this particular problem with yt's before I got mine, so I asked whether the parents had this problem and was told no. So far, so good. Wondering when did this ct show up in Bella? Can it happen at any age?