Hello Henney and GALEX (Welcome),
I have the same worries that you do - so badly in fact I was ready to sell my girls, who I raised from babies, because I didn't want to have to deal with the situations that might arise. I figured to find someone else who will have to deal with the problems that arise from older birds.
But I didn't, in the end, and I'm working on taking things as they happen. My girls are about nine months old, they're healthy and laying well and I'm going to learn to just stop worrying about it. I'm a worrier by nature and the thought of having to cull a bird or deal with them when they're old was keeping me awake at night.
I don't know what I'm going to do in the future with them but I'll deal with it when I get there.
Good luck. Have fun and enjoy them while you have them. I know just what you're going through.
Mary